Creating plots in R using ggplot2 - Parts 1-9

I recently teamed up with Mauricio Vargas Sepúlveda to create some graphing tutorials in R. In the coming weeks, we will be publishing a series of tutorials on how to use the ggplot2 package to create beautiful and informative data visualisations. Each tutorial will explain how to create a different type of plot, and will take you step-by-step from a basic plot to a highly customised graph.

We will demonstrate some of the many options the ggplot2 package has for creating and customising line plots. We will use an international trade dataset (parts 1-4) made by ourselves from different sources (Chile Customs, Central Bank of Chile and General Directorate of International Economic Relations).

Line Plots

The first thing to do is load in the data and libraries, as below:

library(ggplot2)
library(ggthemes)
library(extrafont)

charts.data <- read.csv("copper-data-for-tutorial.csv")

In this part, we will work towards creating the line plot below. We will take you from a basic line plot and explain all the customisations we add to the code step-by-step.

Basic graph

In order to initialise a plot we tell ggplot that charts.data is our data, and specify the variables on each axis. We then instruct ggplot to render this as a line plot by adding the geom_line command.

p1 <- ggplot() + geom_line(aes(y = export, x = year, colour = product), 
                           data = charts.data, stat="identity")
p1

Adjusting line width

To change the line width, we add a size argument to geom_line.

p1 <- ggplot() + geom_line(aes(y = export, x = year, colour = product), size=1.5, 
                           data = charts.data, stat="identity")
p1

Changing variables display

To change the variables displayed name, we need to re-factor our data labels in charts.data data frame. Then we move the legend to the bottom using the theme command.

charts.data <- as.data.frame(charts.data)
charts.data$product <- factor(charts.data$product, levels = c("copper","others"), 
                              labels = c("Copper","Pulp wood, Fruit, Salmon & Others"))

p1 <- ggplot() + 
  geom_line(aes(y = export, x = year, colour = product), size=1.5, data = charts.data, stat="identity") +
  theme(legend.position="bottom", legend.direction="horizontal", legend.title = element_blank())
p1

Adjusting x-axis scale

To change the axis tick marks, we use the scale_x_continuous and/or scale_y_continuous commands.

p1 <- p1 + scale_x_continuous(breaks=seq(2006,2014,1))
p1

Adjusting axis labels & adding title

To add a title, we include the option ggtitle and include the name of the graph as a string argument, and to change the axis names we use the labs command.

p1 <- p1 + ggtitle("Composition of Exports to China ($)") + labs(x="Year", y="USD million") 
p1

Adjusting color palette

To change the colours, we use the scale_colour_manual command.

colour <- c("#5F9EA0", "#E1B378")
p1 <- p1 + scale_colour_manual(values=colour)
p1

Using the white theme

We’ll start using a simple theme customisation made adding theme_bw() after ggplot(). That theme argument can be modified to use different themes.

p1 <- ggplot() +
  geom_line(aes(y = export, x = year, colour = product), size=1.5, data = charts.data, 
            stat="identity") + 
  scale_x_continuous(breaks=seq(2006,2014,1)) + 
  labs(x="Year", y="USD million") + 
  ggtitle("Composition of Exports to China ($)") + 
  scale_colour_manual(values=colour) +
  theme_bw() +
  theme(legend.position="bottom", 
        legend.direction="horizontal", 
        legend.title = element_blank()) 
p1

Creating an XKCD style chart

Of course, you may want to create your own themes as well. ggplot2 allows for a very high degree of customisation, including allowing you to use imported fonts. Below is an example of a theme Mauricio was able to create which mimics the visual style of XKCD. In order to create this chart, you first need to import the XKCD font, install it on your machine and load it into R using the extrafont package. These instructions are taken from here:

library(extrafont)

download.file("http://simonsoftware.se/other/xkcd.ttf", 
              dest="xkcd.ttf", mode="wb")
system("mkdir ~/.fonts")
system("cp xkcd.ttf  ~/.fonts")
font_import(paths = "~/.fonts", pattern="[X/x]kcd")
fonts()
loadfonts()

You can then create your graph:

fill <- c("#56B4E9", "#ff69b4")

p1 <- ggplot() + 
  geom_line(aes(y = export, x = year, colour = product), size=1.5, data = charts.data, 
            stat="identity") + 
  scale_x_continuous(breaks=seq(2006,2014,1)) + 
  labs(x="Year", y="USD million") + 
  ggtitle("Composition of Exports to China ($)") + 
  scale_color_manual(values=fill) + 
  theme(axis.text.x=element_text(colour="black", size = 10), 
        axis.text.y=element_text(colour="black", size = 10),
        axis.line.x = element_line(size=.5, colour = "black"),
        axis.line.y = element_line(size=.5, colour = "black"),
        legend.key=element_rect(fill="white", colour="white"),
        legend.position="bottom", legend.direction="horizontal", 
        legend.title = element_blank(),
        panel.grid.major = element_blank(),
        panel.grid.minor = element_blank(), panel.border = element_blank(), 
        panel.background = element_blank(),
        plot.title=element_text(family="xkcd-Regular"), text=element_text(family="xkcd-Regular")) 
p1

Using ‘The Economist’ theme

There are a wider range of pre-built themes available as part of the ggthemes package (more information on these here). Below we’ve applied theme_economist(), which approximates graphs in the Economist magazine. It is also important that the font change argument inside theme is optional and it’s only to obtain a more similar result compared to the original. For an exact result you need ‘Officina Sans’ which is a commercial font and is available here.

p1 <- ggplot() +
  geom_line(aes(y = export, x = year, colour = product), size=1.5, data = charts.data, 
            stat="identity") + 
  scale_x_continuous(breaks=seq(2006,2014,1)) + 
  labs(x="Year", y="USD million") + 
  ggtitle("Composition of Exports to China ($)") +
  theme_economist() + scale_colour_economist() +
  theme(axis.line.x = element_line(size=.5, colour = "black"), 
        axis.line.y = element_line(size=.5, colour = "black"),
        legend.position="bottom", 
        legend.direction="horizontal", 
        legend.title = element_blank(),
        plot.title=element_text(family="OfficinaSanITC-Book"),
        text=element_text(family="OfficinaSanITC-Book")) 
p1

Creating your own theme

As before, you can modify your plots a lot as ggplot2 allows many customisations. Here we present our original result shown at the top of page.

colour <- c("#40b8d0", "#b2d183")

p1 <- ggplot() + 
  geom_line(aes(y = export, x = year, colour = product), size=1.5, data = charts.data, 
            stat="identity") + 
  scale_x_continuous(breaks=seq(2006,2014,1)) + 
  labs(x="Year", y="USD million") + 
  ggtitle("Composition of Exports to China ($)") + 
  scale_colour_manual(values=colour) + 
  theme(axis.line.x = element_line(size=.5, colour = "black"), 
        axis.line.y = element_line(size=.5, colour = "black"), 
        axis.text.x=element_text(colour="black", size = 10), 
        axis.text.y=element_text(colour="black", size = 10),
        legend.key=element_rect(fill="white", colour="white"),
        legend.position="bottom", legend.direction="horizontal", 
        legend.title = element_blank(),
        panel.grid.major = element_line(colour = "#d3d3d3"), 
        panel.grid.minor = element_blank(), 
        panel.border = element_blank(), 
        panel.background = element_blank(),
        plot.title = element_text(size = 14, family = "Tahoma", face = "bold"), 
        text=element_text(family="Tahoma")) 
p1

Area Plots

In this part, we will work towards creating the area plot below. We will take you from a basic area plot and explain all the customisations we add to the code step-by-step.

Basic graph

The first thing to do is load in the data and libraries, as below:

library(ggplot2)
library(ggthemes)
library(extrafont)
library(plyr)
charts.data <- read.csv("copper-data-for-tutorial.csv")

In order to initialise a plot we tell ggplot that charts.data is our data, and specify the variables on each axis. We then instruct ggplot to render this as an area plot by adding the geom_area command.

charts.data <- read.csv("copper-data-for-tutorial.csv")

p2 <- ggplot() + geom_area(aes(y = export, x = year, fill = product), data = charts.data, 
                           stat="identity")
p2

Adjusting legend position

To adjust the position of the legend from the default spot of right of the graph, we add the theme option and specify the legend.position="bottom" argument. We can also change the title to blank using the legend.title = element_blank() argument and change the legend shape using the legend.direction="horizontal" argument.

charts.data <- ddply(charts.data, .(year), transform, pos = cumsum(export) - (0.5 * export))

p2 <- p2 + theme(legend.position="bottom", legend.direction="horizontal", legend.title = element_blank())
p2

Changing variables display

To change the variables displayed name, we need to re-factor our data labels in charts.data data frame.

charts.data <- as.data.frame(charts.data)
charts.data$product <- factor(charts.data$product, levels = c("copper","others"), 
                              labels = c("Copper","Pulp wood, Fruit, Salmon & Others"))

p2 <- ggplot() + 
  geom_area(aes(y = export, x = year, fill = product), data = charts.data, stat="identity") + 
  theme(legend.position="bottom", legend.direction="horizontal", legend.title = element_blank())
p2

Adjusting x-axis scale

To change the axis tick marks, we use the scale_x_continuous and/or scale_y_continuous commands.

p2 <- p2 + scale_x_continuous(breaks=seq(2006,2014,1))
p2

Adjusting axis labels & adding title

To add a title, we include the option ggtitle and include the name of the graph as a string argument, and to change the axis names we use the labs command.

p2 <- p2 + ggtitle("Composition of Exports to China ($)") + 
            labs(x="Year", y="USD million") 
p2

Adjusting color palette

To change the colours, we use the scale_colour_manual command. Note that you can reference the specific colours you’d like to use with specific HEX codes. You can also reference colours by name, with the full list of colours recognised by R here.

fill <- c("#5F9EA0", "#E1B378")
p2 <- p2 + scale_fill_manual(values=fill)
p2

Using the white theme

As explained in the previous post, we can also change the overall look of the site using themes. We’ll start using a simple theme customisation by adding theme_bw() after ggplot(). As you can see, we can further tweak the graph using the theme option, which we’ve used so far to change the legend.

p2 <- ggplot() +
  geom_area(aes(y = export, x = year, fill = product), data = charts.data, 
            stat="identity") + 
  scale_x_continuous(breaks=seq(2006,2014,1)) + 
  labs(x="Year", y="USD million") + 
  ggtitle("Composition of Exports to China ($)") + 
  scale_fill_manual(values=fill) +
  theme_bw() +
  theme(legend.position="bottom", 
        legend.direction="horizontal", 
        legend.title = element_blank())   
p2

Creating an XKCD style chart

Of course, you may want to create your own themes as well. ggplot2 allows for a very high degree of customisation, including allowing you to use imported fonts. Below is an example of a theme Mauricio was able to create which mimics the visual style of XKCD. In order to create this chart, you first need to import the XKCD font, install it on your machine and load it into R using the extrafont package. These instructions are taken from here:

library(extrafont)

download.file("http://simonsoftware.se/other/xkcd.ttf", 
              dest="xkcd.ttf", mode="wb")
system("mkdir ~/.fonts")
system("cp xkcd.ttf  ~/.fonts")
font_import(paths = "~/.fonts", pattern="[X/x]kcd")
fonts()
loadfonts()

You can then create your graph:

fill <- c("#56B4E9", "#ff69b4")

p2 <- ggplot() + 
  geom_area(aes(y = export, x = year, fill = product), data = charts.data, stat="identity") + 
  scale_x_continuous(breaks=seq(2006,2014,1)) + 
  labs(x="Year", y="USD million") + 
  ggtitle("Composition of Exports to China ($)") + 
  scale_fill_manual(values=fill) + 
  theme(axis.text.x=element_text(colour="black", size = 10), 
        axis.text.y=element_text(colour="black", size = 10),
        axis.line.x = element_line(size=.5, colour = "black"),
        axis.line.y = element_line(size=.5, colour = "black"),
        legend.key=element_rect(fill="white", colour="white"),
        legend.position="bottom", legend.direction="horizontal", 
        legend.title = element_blank(),
        panel.grid.major = element_blank(),
        panel.grid.minor = element_blank(), panel.border = element_blank(), 
        panel.background = element_blank(),
        plot.title=element_text(family="xkcd-Regular"), text=element_text(family="xkcd-Regular")) 
p2

Using ‘The Economist’ theme

There are a wider range of pre-built themes available as part of the ggthemes package (more information on these here). Below we’ve applied theme_economist(), which approximates graphs in the Economist magazine. It is also important that the font change argument inside theme is optional and it’s only to obtain a more similar result compared to the original. For an exact result you need ‘Officina Sans’ which is a commercial font and is available here.

p2 <- ggplot() +
  geom_area(aes(y = export, x = year, fill = product), data = charts.data, stat="identity") + 
  scale_x_continuous(breaks=seq(2006,2014,1)) + 
  labs(x="Year", y="USD million") + 
  ggtitle("Composition of Exports to China ($)") +
  theme_economist() + scale_fill_economist() +
  theme(axis.line.x = element_line(size=.5, colour = "black"), 
        axis.line.y = element_line(size=.5, colour = "black"),
        legend.position="bottom", 
        legend.direction="horizontal", 
        legend.title = element_blank(),
        plot.title=element_text(family="OfficinaSanITC-Book"),
        text=element_text(family="OfficinaSanITC-Book"))   
p2

Creating your own theme

As before, you can modify your plots a lot as ggplot2 allows many customisations. Here we present our original result shown at the top of page.

fill <- c("#40b8d0", "#b2d183")

p2 <- ggplot() + 
  geom_area(aes(y = export, x = year, fill = product), data = charts.data, 
            stat="identity") + 
  scale_x_continuous(breaks=seq(2006,2014,1)) + 
  labs(x="Year", y="USD million") + 
  ggtitle("Composition of Exports to China ($)") + 
  scale_fill_manual(values=fill) + 
  theme(axis.line.x = element_line(size=.5, colour = "black"), 
        axis.line.y = element_line(size=.5, colour = "black"), 
        axis.text.x=element_text(colour="black", size = 10), 
        axis.text.y=element_text(colour="black", size = 10),
        legend.key=element_rect(fill="white", colour="white"),
        legend.position="bottom", legend.direction="horizontal", 
        legend.title = element_blank(),
        panel.grid.major = element_line(colour = "#d3d3d3"), 
        panel.grid.minor = element_blank(), 
        panel.border = element_blank(), 
        panel.background = element_blank(),
        plot.title = element_text(size = 14, family = "Tahoma", face = "bold"), 
        text=element_text(family="Tahoma"))
p2

Bar Plots

In this part, we will work towards creating the area plot below. We will take you from a basic bar plot and explain all the customisations we add to the code step-by-step.

Basic graph

The first thing to do is load in the data and libraries, as below:

library(ggplot2)
library(ggthemes)
library(extrafont)
library(plyr)
library(scales)
charts.data <- read.csv("copper-data-for-tutorial.csv")

In order to initialise a plot we tell ggplot that charts.data is our data, and specify the variables on each axis. We then instruct ggplot to render this as an bar plot by adding the geom_area command.

p3 <- ggplot() + geom_bar(aes(y = export, x = year, fill = product), data = charts.data, 
                          stat="identity")
p3

Adding data labels

To label the bars according to some variable in the data, we add the label argument to the ggplot(aes()) option. In this case, we have labelled the bars with numbers from the export variable.

p3 <- p3 + geom_text(data=charts.data, aes(x = year, y = export, label = export), size=4)
p3

Adjusting data labels position

To adjust the position of the data labels from the default placement, we use the ddply function on the data, and create a new variable called pos. This variable is at the centre of each bar and can be used to specify the position of the labels by assigning it to the y argument in geom_text(aes()).

charts.data <- ddply(charts.data, .(year), transform, pos = cumsum(export) - (0.5 * export))

p3 <- ggplot() + geom_bar(aes(y = export, x = year, fill = product), data = charts.data, 
                          stat="identity") 
p3 <- p3 + geom_text(data=charts.data, aes(x = year, y = pos, label = export), size=4)
p3

Adjusting legend position

To adjust the position of the legend from the default spot of right of the graph, we add the theme option and specify the legend.position="bottom" argument. We can also change the title to blank using the legend.title = element_blank() argument and change the legend shape using the legend.direction="horizontal" argument.

p3 <- p3 + theme(legend.position="bottom", legend.direction="horizontal", 
                 legend.title = element_blank())
p3

Changing variables display

To change the variables’ displayed name, we need to re-factor our data labels in charts.data data frame.

charts.data$product <- factor(charts.data$product, levels = c("copper","others"), 
                              labels = c("Copper","Pulp wood, Fruit, Salmon & Others"))

p3 <- ggplot() + geom_bar(aes(y = export, x = year, fill = product), data = charts.data, 
                          stat="identity") + 
      geom_text(data=charts.data, aes(x = year, y = pos, label = export, size=4), 
                show.legend = F) + 
      theme(legend.position="bottom", legend.direction="horizontal", legend.title = element_blank())
p3

Adjusting x-axis scale

To change the axis tick marks, we use the scale_x_continuous and/or scale_y_continuous commands.

p3 <- p3 + scale_x_continuous(breaks=seq(2006,2014,1))
p3

Adjusting axis labels & adding title

To add a title, we include the option ggtitle and include the name of the graph as a string argument, and to change the axis names we use the labs command.

p3 <- p3 + ggtitle("Composition of Exports to China ($)") + labs(x="Year", y="USD million") 
p3

Adjusting color palette

To change the colours, we use the scale_colour_manual command. Note that you can reference the specific colours you’d like to use with specific HEX codes. You can also reference colours by name, with the full list of colours recognised by R here.

fill <- c("#5F9EA0", "#E1B378")
p3 <- p3 + scale_fill_manual(values=fill)
p3

Using the white theme

As explained in the previous posts, we can also change the overall look of the graph using themes. We’ll start using a simple theme customisation by adding theme_bw() after ggplot(). As you can see, we can further tweak the graph using the theme option, which we’ve used so far to change the legend.

p3 <- ggplot() +
  geom_bar(aes(y = export, x = year, fill = product), data = charts.data, stat="identity") + 
  geom_text(data=charts.data, aes(x = year, y = pos, label = export, size=4), show.legend = F) + 
  scale_x_continuous(breaks=seq(2006,2014,1)) + 
  labs(x="Year", y="USD million") + 
  ggtitle("Composition of Exports to China ($)") + 
  scale_fill_manual(values=fill) +
  theme_bw() +
  theme(legend.position="bottom", 
        legend.direction="horizontal", 
        legend.title = element_blank())   
p3

Creating an XKCD style chart

Of course, you may want to create your own themes as well. ggplot2 allows for a very high degree of customisation, including allowing you to use imported fonts. Below is an example of a theme Mauricio was able to create which mimics the visual style of XKCD. In order to create this chart, you first need to import the XKCD font, install it on your machine and load it into R using the extrafont package. These instructions are taken from here:

library(extrafont)

download.file("http://simonsoftware.se/other/xkcd.ttf", 
              dest="xkcd.ttf", mode="wb")
system("mkdir ~/.fonts")
system("cp xkcd.ttf  ~/.fonts")
font_import(paths = "~/.fonts", pattern="[X/x]kcd")
fonts()
loadfonts()

You can then create your graph:

fill <- c("#56B4E9", "#F0E442")

p3 <- ggplot() + 
  geom_bar(aes(y = export, x = year, fill = product), data = charts.data, stat="identity") + 
  geom_text(data=charts.data, aes(x = year, y = pos, label = export), colour="black", 
            family="xkcd-Regular", size = 4, show.legend = F) + 
  scale_x_continuous(breaks=seq(2006,2014,1)) + 
  labs(x="Year", y="USD million") + 
  ggtitle("Composition of Exports to China ($)") + 
  scale_fill_manual(values=fill) + 
  theme(axis.text.x=element_text(colour="black", size = 10), 
        axis.text.y=element_text(colour="black", size = 10),
        axis.line.x = element_line(size=.5, colour = "black"),
        axis.line.y = element_line(size=.5, colour = "black"),
        legend.key=element_rect(fill="white", colour="white"),
        legend.position="bottom", legend.direction="horizontal", 
        legend.title = element_blank(),
        panel.grid.major = element_blank(),
        panel.grid.minor = element_blank(), panel.border = element_blank(), 
        panel.background = element_blank(),
        plot.title=element_text(family="xkcd-Regular"), text=element_text(family="xkcd-Regular")) 
p3

Using ‘The Economist’ theme

There are a wider range of pre-built themes available as part of the ggthemes package (more information on these here). Below we’ve applied theme_economist(), which approximates graphs in the Economist magazine. It is also important that the font change argument inside theme is optional and it’s only to obtain a more similar result compared to the original. For an exact result you need ‘Officina Sans’ which is a commercial font and is available here.

p3 <- ggplot() +
  geom_bar(aes(y = export, x = year, fill = product), data = charts.data, 
           stat="identity") + 
  geom_text(data=charts.data, aes(x = year, y = pos, label = export), colour="white", size = 4,
            family = "OfficinaSanITC-Book", show.legend = F) + 
  scale_x_continuous(breaks=seq(2006,2014,1)) + 
  labs(x="Year", y="USD million") + 
  ggtitle("Composition of Exports to China ($)") +
  theme_economist() + scale_fill_economist() +
  theme(axis.line.x = element_line(size=.5, colour = "black"), 
        axis.line.y = element_line(size=.5, colour = "black"),
        legend.position="bottom", 
        legend.direction="horizontal", 
        legend.title = element_blank(),
        plot.title=element_text(family="OfficinaSanITC-Book"),
        text=element_text(family="OfficinaSanITC-Book"))   
p3

Creating your own theme

As before, you can modify your plots a lot as ggplot2 allows many customisations. Here we present our original result shown at the top of page.

fill <- c("#40b8d0", "#b2d183")

p3 <- ggplot() + 
  geom_bar(aes(y = export, x = year, fill = product), data = charts.data, stat="identity") + 
  geom_text(data=charts.data, aes(x = year, y = pos, label = export), colour="black", 
            family="Tahoma", size = 4, show.legend = F) + 
  scale_x_continuous(breaks=seq(2006,2014,1)) + 
  labs(x="Year", y="USD million") + 
  ggtitle("Composition of Exports to China ($)") + 
  scale_fill_manual(values=fill) + 
  theme(axis.line.x = element_line(size=.5, colour = "black"), 
        axis.line.y = element_line(size=.5, colour = "black"), 
        axis.text.x=element_text(colour="black", size = 10), 
        axis.text.y=element_text(colour="black", size = 10),
        legend.key=element_rect(fill="white", colour="white"),
        legend.position="bottom", legend.direction="horizontal", 
        legend.title = element_blank(),
        panel.grid.major = element_line(colour = "#d3d3d3"), 
        panel.grid.minor = element_blank(), 
        panel.border = element_blank(), 
        panel.background = element_blank(),
        plot.title = element_text(size = 14, family = "Tahoma", face = "bold"), 
        text=element_text(family="Tahoma"))  
p3

Stacked Bar Plots

In this part, we will work towards creating the bar plot below. We will take you from a basic stacked bar plot and explain all the customisations we add to the code step-by-step.

Basic graph

In order to initialise a plot we tell ggplot that charts.data is our data, and specify the variables on each axis. We then instruct ggplot to render this as a stacked bar plot by adding the geom_bar command.

The first thing to do is load in the data and libraries, as below:

library(ggplot2)
library(ggthemes)
library(extrafont)
library(plyr)
library(scales)
charts.data <- read.csv("copper-data-for-tutorial.csv")

charts.data <- read.csv("copper-data-for-tutorial.csv")

p4 <- ggplot() + geom_bar(aes(y = percentage, x = year, fill = product), data = charts.data, 
                          stat="identity")
p4

Adding data labels

To label the bars according to some variable in the data, we add the label argument to the ggplot(aes()) option. In this case, we have labelled the bars with numbers from the export variable.

p4 <- p4 + geom_text(data=charts.data, aes(x = year, y = percentage, 
                                           label = paste0(percentage,"%")), size=4)
p4

Adjusting data labels position

To adjust the position of the data labels from the default placement, we use the ddply function on the data, and create a new variable called pos. This variable is at the centre of each bar and can be used to specify the position of the labels by assigning it to the y argument in geom_text(aes()).

charts.data <- ddply(charts.data, .(year), transform, pos = cumsum(percentage) - (0.5 * percentage))

p4 <- ggplot() + geom_bar(aes(y = percentage, x = year, fill = product), data = charts.data,
                          stat="identity")
p4 <- p4 + geom_text(data=charts.data, aes(x = year, y = pos, label = paste0(percentage,"%")),
                     size=4)
p4

Adjusting legend position

To adjust the position of the legend from the default spot of right of the graph, we add the theme option and specify the legend.position="bottom" argument. We can also change the title to blank using the legend.title = element_blank() argument and change the legend shape using the legend.direction="horizontal" argument.

p4 <- p4 + theme(legend.position="bottom", legend.direction="horizontal", 
                 legend.title = element_blank())
p4

Changing variables display

To change the variables’ displayed name, we need to re-factor our data labels in charts.data data frame.

charts.data <- as.data.frame(charts.data)
charts.data$product <- factor(charts.data$product, levels = c("copper","others"), 
                              labels = c("Copper","Pulp wood, Fruit, Salmon & Others"))

p4 <- ggplot() + 
      geom_bar(aes(y = percentage, x = year, fill = product), data = charts.data, stat="identity") + 
      geom_text(data=charts.data, aes(x = year, y = pos, label = paste0(percentage,"%")), size=4) +
      theme(legend.position="bottom", legend.direction="horizontal", legend.title = element_blank())
p4

Adjusting x-axis scale

To change the axis tick marks, we use the scale_x_continuous and/or scale_y_continuous commands.

p4 <- p4 + scale_x_continuous(breaks=seq(2006,2014,1))
p4

Adjusting axis, title & units

To add a title, we include the option ggtitle and include the name of the graph as a string argument, and to change the axis names we use the labs command.

p4 <- p4 + labs(x="Year", y="Percentage") + 
      scale_y_continuous(labels = dollar_format(suffix = "%", prefix = "")) +
      ggtitle("Composition of Exports to China (%)") 
p4

Adjusting color palette

To change the colours, we use the scale_colour_manual command. Note that you can reference the specific colours you’d like to use with specific HEX codes. You can also reference colours by name, with the full list of colours recognised by R here.

fill <- c("#5F9EA0", "#E1B378")
p4 <- p4 + scale_fill_manual(values=fill)
p4

Using the white theme

As explained in the previous posts, we can also change the overall look of the graph using themes. We’ll start using a simple theme customisation by adding theme_bw() after ggplot(). As you can see, we can further tweak the graph using the theme option, which we’ve used so far to change the legend.

p4 <- ggplot() + 
      geom_bar(aes(y = percentage, x = year, fill = product), data = charts.data, stat="identity") + 
      geom_text(data=charts.data, aes(x = year, y = pos, label = paste0(percentage,"%")), size=4) + 
      scale_x_continuous(breaks=seq(2006,2014,1)) + 
      scale_y_continuous(labels = dollar_format(suffix = "%", prefix = "")) + 
      labs(x="Year", y="Percentage") + 
      ggtitle("Composition of Exports to China (%)") +
      theme_bw() +
      theme(legend.position="bottom", 
            legend.direction="horizontal", 
            legend.title = element_blank())    
p4

Creating an XKCD style chart

Of course, you may want to create your own themes as well. ggplot2 allows for a very high degree of customisation, including allowing you to use imported fonts. Below is an example of a theme Mauricio was able to create which mimics the visual style of XKCD. In order to create this chart, you first need to import the XKCD font, install it on your machine and load it into R using the extrafont package. These instructions are taken from here:

library(extrafont)

download.file("http://simonsoftware.se/other/xkcd.ttf", 
              dest="xkcd.ttf", mode="wb")
system("mkdir ~/.fonts")
system("cp xkcd.ttf  ~/.fonts")
font_import(paths = "~/.fonts", pattern="[X/x]kcd")
fonts()
loadfonts()

You can then create your graph:

#font_import(pattern="[X/x]kcd")
#fonts()

fill <- c("#56B4E9", "#F0E442")

p4 <- ggplot() + 
      geom_bar(aes(y = percentage, x = year, fill = product), data = charts.data, stat="identity") + 
      geom_text(data=charts.data, aes(x = year, y = pos, label = paste0(percentage,"%")), 
                colour="black", family="xkcd-Regular", size = 5, show.legend = F) + 
      scale_x_continuous(breaks=seq(2006,2014,1)) + 
      scale_y_continuous(labels = dollar_format(suffix = "%", prefix = "")) + 
      labs(x="Year", y="Percentage") + 
      ggtitle("Composition of Exports to China (%)") + 
      scale_fill_manual(values=fill) + 
      theme(axis.text.x=element_text(colour="black", size = 10), 
            axis.text.y=element_text(colour="black", size = 10),
            axis.line.x = element_line(size=.5, colour = "black"),
            axis.line.y = element_line(size=.5, colour = "black"),
            legend.key=element_rect(fill="white", colour="white"),
            legend.position="bottom", legend.direction="horizontal", 
            legend.title = element_blank(),
            panel.grid.major = element_blank(),
            panel.grid.minor = element_blank(), panel.border = element_blank(), 
            panel.background = element_blank(),
            plot.title=element_text(family="xkcd-Regular"), text=element_text(family="xkcd-Regular")) 
p4

Using ‘The Economist’ theme

There are a wider range of pre-built themes available as part of the ggthemes package (more information on these here). Below we’ve applied theme_economist(), which approximates graphs in the Economist magazine. It is also important that the font change argument inside theme is optional and it’s only to obtain a more similar result compared to the original. For an exact result you need ‘Officina Sans’ which is a commercial font and is available here.

p4 <- ggplot() +
      geom_bar(aes(y = percentage, x = year, fill = product), data = charts.data, stat="identity") + 
      geom_text(data=charts.data, aes(x = year, y = pos, label = paste0(percentage,"%")), 
                colour="white", family="OfficinaSanITC-Book", size=4) + 
      scale_x_continuous(breaks=seq(2006,2014,1)) + 
      scale_y_continuous(labels = dollar_format(suffix = "%", prefix = "")) + 
      labs(x="Year", y="Percentage") + 
      ggtitle("Composition of Exports to China (%)") +
      theme_economist() + scale_fill_economist() + 
      theme(axis.line.x = element_line(size=.5, colour = "black"), 
            axis.line.y = element_line(size=.5, colour = "black"),
            legend.position="bottom", 
            legend.direction="horizontal", 
            legend.title = element_blank(),
            plot.title=element_text(family="OfficinaSanITC-Book"),
            text=element_text(family="OfficinaSanITC-Book"))    
p4

Creating your own theme

As before, you can modify your plots a lot as ggplot2 allows many customisations. Here we present our original result shown at the top of page.

fill <- c("#40b8d0", "#b2d183")

p4 <- ggplot() + 
      geom_bar(aes(y = percentage, x = year, fill = product), data = charts.data, stat="identity") + 
      geom_text(data=charts.data, aes(x = year, y = pos, label = paste0(percentage,"%")), 
            colour="black", family="Tahoma", size=4) + 
      scale_x_continuous(breaks=seq(2006,2014,1)) + 
      scale_y_continuous(labels = dollar_format(suffix = "%", prefix = "")) + 
      labs(x="Year", y="Percentage") + 
      ggtitle("Composition of Exports to China (%)") + 
      scale_fill_manual(values=fill) + 
      theme(axis.line.x = element_line(size=.5, colour = "black"), 
            axis.line.y = element_line(size=.5, colour = "black"), 
            axis.text.x=element_text(colour="black", size = 10), 
            axis.text.y=element_text(colour="black", size = 10),
            legend.key=element_rect(fill="white", colour="white"),
            legend.position="bottom", legend.direction="horizontal", 
            legend.title = element_blank(),
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), 
            panel.background = element_blank(),
            plot.title = element_text(size = 14, family = "Tahoma", face = "bold"), 
            text=element_text(family="Tahoma")) 
p4

Scatter Plots

In this part, we will work towards creating the scatterplot below. We will take you from a basic scatterplot and explain all the customisations we add to the code step-by-step.

The first thing to do is load in the data, as below:

library(ggplot2)
library(ggthemes)
library(extrafont)
library(datasets)
data(airquality)

We will then trim the data down to the final three months and turn the Month variable into a labelled factor variable. We end up with a new dataset called aq_trim.

aq_trim <- airquality[which(airquality$Month == 7 |
airquality$Month == 8 |
airquality$Month == 9), ]
aq_trim$Month <- factor(aq_trim$Month, 
labels = c("July", "August", "September"))

Basic scatterplot

In order to initialise a scatterplot we tell ggplot that aq_trim is our data, and specify that our x-axis plots the Day variable and our y-axis plots the Ozone variable. We then instruct ggplot to render this as a scatterplot by adding the geom_point() option.

p5 <- ggplot(aq_trim, aes(x = Day, y = Ozone)) + 
      geom_point()
p5

Changing the shape of the data points

Perhaps we want the data points to be a different shape than a solid circle. We can change these by adding the shape argument to geom_point. An explanation of the allowed arguments for shape are described in this article. In this case, we will use shape 21, which is a circle that allows different colours for the outline and fill.

p5 <- ggplot(aq_trim, aes(x = Day, y = Ozone)) + geom_point(shape = 21)
p5

Adjusting the axis scales

To change the x-axis tick marks, we use the scale_x_continuous option. Similarly, to change the y-axis we use the scale_y_continuous option. Here we will change the x-axis to every 5 days, rather than 10, and change the range from 1 to 31 (as 0 is not a valid value for this variable).

p5 <- p5 + scale_x_continuous(breaks = seq(1, 31, 5))
p5

Adjusting axis labels & adding title

To add a title, we include the option ggtitle and include the name of the graph as a string argument. To change the axis names we add x and y arguments to the labs command.

p5 <- p5 + ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)") 
p5

Adjusting the colour palette

There are a few options for adjusting the colour. The most simple is to make every point one fixed colour. You can reference colours by name, with the full list of colours recognised by R here. Let’s try making the outline mediumvioletred and the fill springgreen.

p5 <- ggplot(aq_trim, aes(x = Day, y = Ozone)) + 
      geom_point(shape = 21, colour = "mediumvioletred", fill = "springgreen") +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)") +
      scale_x_continuous(breaks = seq(1, 31, 5)) 
p5

You can change the colours using specific HEX codes instead. Here we have made the outline #000000 (black) and the fill “#40b8d0 (vivid cyan).

p5 <- ggplot(aq_trim, aes(x = Day, y = Ozone)) + 
      geom_point(shape = 21, colour = "#000000", fill = "#40b8d0") +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)") +
      scale_x_continuous(breaks = seq(1, 31, 5))
p5

You can also change the colour of the data points according to the levels of another variable. This can be done either as a continuous gradient, or as a levels of a factor variable. Let’s change the colour by the values of temperature:

p5 <- ggplot(aq_trim, aes(x = Day, y = Ozone, fill = Temp)) + 
      geom_point(shape = 21) +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)") +
      scale_x_continuous(breaks = seq(1, 31, 5))
p5

We can change the gradient’s colours by adding the scale_fill_continuous option. The low and high arguments specify the range of colours the gradient should transition between.

p5 <-  p5 + scale_fill_continuous(low = "plum1", high = "purple4")
p5

We can see that higher temperatures seem to have higher ozone levels.

Let’s now change the colours of the data points by a factor variable, Month.

p5 <- ggplot(aq_trim, aes(x = Day, y = Ozone, fill = Month)) + 
      geom_point(shape = 21) +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)") +
      scale_x_continuous(breaks = seq(1, 31, 5))
p5

Again, we can change the colours of these data points, this time using scale_fill_manual.

fill = c("steelblue", "yellowgreen", "violetred1")

p5 <- p5 + scale_fill_manual(values = fill)
p5

Adjusting legend position

To adjust the position of the legend from the default spot of right of the graph, we add the theme option and specify the legend.position = "bottom" argument. We can also change the legend shape using the legend.direction = "horizontal" argument.

p5 <- p5 + theme(legend.position = "bottom", legend.direction = "horizontal")
p5

Using the white theme

As explained in the previous posts, we can also change the overall look of the plot using themes. We’ll start using a simple theme customisation by adding theme_bw() after ggplot(). As you can see, we can further tweak the graph using the theme option, which we’ve used so far to change the legend.

p5 <- ggplot(aq_trim, aes(x = Day, y = Ozone, fill = Month)) + theme_bw() +
      geom_point(shape = 21) +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)", fill = "Months") +
      scale_x_continuous(breaks = seq(1, 31, 5)) +
      scale_fill_manual(values = fill) +
      scale_size(range = c(1, 10)) +
      theme(legend.position="bottom", legend.direction="horizontal")
p5

Creating an XKCD style chart

Of course, you may want to create your own themes as well. ggplot2 allows for a very high degree of customisation, including allowing you to use imported fonts. Below is an example of a theme Mauricio was able to create which mimics the visual style of XKCD. In order to create this chart, you first need to import the XKCD font, install it on your machine and load it into R using the extrafont package. These instructions are taken from here:

library(extrafont)

download.file("http://simonsoftware.se/other/xkcd.ttf", dest="xkcd.ttf", mode="wb")
system("mkdir ~/.fonts")
system("cp xkcd.ttf  ~/.fonts")
font_import(paths = "~/.fonts", pattern="[X/x]kcd")
fonts()
loadfonts()

You can then create your graph:

fill <- c("#56B4E9", "#F0E442", "violetred1")

p5 <- ggplot(aq_trim, aes(x = Day, y = Ozone, fill = Month)) + 
      geom_point(shape = 21) +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)", fill = "Months") +
      scale_x_continuous(breaks = seq(1, 31, 5)) +
      scale_fill_manual(values = fill) +
      scale_size(range = c(1, 10)) +
      theme(axis.line.x = element_line(size=1, colour = "black"),
            axis.line.y = element_line(size=1, colour = "black"),
            axis.text.x=element_text(colour="black", size = 10), 
            axis.text.y=element_text(colour="black", size = 10), 
            legend.position="bottom", legend.direction="horizontal",
            panel.grid.major = element_blank(),
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(),
            panel.background = element_blank(),
            plot.title=element_text(family="xkcd-Regular"), 
            text=element_text(family="xkcd-Regular")) 
p5

Using ‘The Economist’ theme

There are a wider range of pre-built themes available as part of the ggthemes package (more information on these here). Below we’ve applied theme_economist(), which approximates graphs in the Economist magazine.

p5 <- ggplot(aq_trim, aes(x = Day, y = Ozone, fill = Month)) +
      scale_fill_economist() +
      geom_point(shape = 21) +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)", fill = "Months") +
      scale_x_continuous(breaks = seq(1, 31, 5)) +
      scale_size(range = c(1, 10)) +
      theme_economist() + 
      theme(axis.line.x = element_line(size=.5, colour = "black"), 
            axis.line.y = element_line(size=.5, colour = "black"), 
            axis.title = element_text(size = 12),
            legend.position = "bottom", legend.direction = "horizontal",
            legend.text = element_text(size = 9),
            legend.title=element_text(face = "bold", size = 9),
            text = element_text(family = "Tahoma"),  
            plot.title = element_text(family="Tahoma"))
p5

Creating your own theme

As before, you can modify your plots a lot as ggplot2 allows many customisations. Here we present our original result shown at the top of page.

fill = c("steelblue", "yellowgreen", "violetred1")

p5 <- ggplot(aq_trim, aes(x = Day, y = Ozone, fill = Month)) +
      geom_point(shape = 21) +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)", fill = "Months") +
      scale_x_continuous(breaks = seq(1, 31, 5)) +
      scale_size(range = c(1, 10)) +
      scale_fill_manual(values = fill) +
      theme(axis.line.x = element_line(size=1, colour = "black"), 
            axis.line.y = element_line(size=1, colour = "black"), 
            axis.text.x=element_text(colour="black", size = 9), 
            axis.text.y=element_text(colour="black", size = 9),  
            legend.position = "bottom", legend.direction = "horizontal",
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), panel.background = element_blank(),
            plot.title = element_text(size = 14, family = "Tahoma", face = "bold"),
            text=element_text(family="Tahoma")) 
p5

Weighted Scatter Plots

The first thing to do is load in the data, as below:

rm(list = ls())
library(datasets)
library(ggplot2)
data(airquality)

We will then trim the data down to the final three months and turn the Month variable into a labelled factor variable. We end up with a new dataset called aq_trim.

aq_trim <- airquality[which(airquality$Month == 7 |
airquality$Month == 8 |
airquality$Month == 9), ]
aq_trim$Month <- factor(aq_trim$Month, 
labels = c("July", "August", "September"))

In this part, we will work towards creating the weighted scatterplot below. We will take you from a basic scatterplot and explain all the customisations we add to the code step-by-step.

Basic weighted scatterplot

Let’s start really slowly by revisiting how to create a basic scatterplot. In order to initialise this plot we tell ggplot that aq_trim is our data, and specify that our x-axis plots the Day variable and our y-axis plots the Ozone variable. We then instruct ggplot to render this as a scatterplot by adding the geom_point() option.

p6 <- ggplot(aq_trim, aes(x = Day, y = Ozone)) + 
      geom_point()
p6

In order to turn this into a weighted scatterplot, we simply add the size argument to ggplot(aes()). In this case, we want to weight the points by the Wind variable.

p6 <- ggplot(aq_trim, aes(x = Day, y = Ozone, size = Wind)) + 
      geom_point()
p6

You can see we already have an interesting looking pattern, where days with higher wind speed tend to have lower ozone (or in other words, better air quality). Now let’s make it beautiful!

Changing the shape of the data points

Perhaps we want the data points to be a different shape than a solid circle. We can change these by adding the shape argument to geom_point. An explanation of the allowed arguments for shape are described in this article. In this case, we will use shape 21, which is a circle that allows different colours for the outline and fill.

p6 <- ggplot(aq_trim, aes(x = Day, y = Ozone, size = Wind)) + 
      geom_point(shape = 21)
p6

Adjusting the axis scales

To change the x-axis tick marks, we use the scale_x_continuous option. Similarly, to change the y-axis we use the scale_y_continuous option. Here we will change the x-axis to every 5 days, rather than 10, and change the range from 1 to 31 (as 0 is not a valid value for this variable).

p6 <- p6 + scale_x_continuous(breaks = seq(1, 31, 5))
p6

Adjusting axis labels & adding title

To add a title, we include the option ggtitle and include the name of the graph as a string argument. To change the axis names we add x and y arguments to the labs command.

p6 <- p6 + ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)") 
p6

Adjusting the colour palette

There are a few options for adjusting the colour. The most simple is to make every point one fixed colour. You can reference colours by name, with the full list of colours recognised by R here. Let’s try making the outline mediumvioletred and the fill springgreen.

p6 <- ggplot(aq_trim, aes(x = Day, y = Ozone, size = Wind)) + 
      geom_point(shape = 21, colour = "mediumvioletred", 
       fill = "springgreen") +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)") +
      scale_x_continuous(breaks = seq(1, 31, 5)) 
p6

You can change the colours using specific HEX codes instead. Here we have made the outline #000000 (black) and the fill “#40b8d0 (vivid cyan).

p6 <- ggplot(aq_trim, aes(x = Day, y = Ozone, size = Wind)) + 
      geom_point(shape = 21, colour = "#000000", fill = "#40b8d0") +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)") +
      scale_x_continuous(breaks = seq(1, 31, 5))
p6

You can also change the colour of the data points according to the levels of another variable. This can be done either as a continuous gradient, or as a levels of a factor variable. Let’s change the colour by the values of temperature:

p6 <- ggplot(aq_trim, aes(x = Day, y = Ozone, size = Wind, fill = Temp)) + 
      geom_point(shape = 21) +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)") +
      scale_x_continuous(breaks = seq(1, 31, 5))
p6

We can change the gradient’s colours by adding the scale_fill_continuous option. The low and high arguments specify the range of colours the gradient should transition between.

p6 <-p6 + scale_fill_continuous(low = "plum1", high = "purple4")
p6

We can see that higher temperatures seem to have higher ozone levels.

Let’s now change the colours of the data points by a factor variable, Month.

p6 <- ggplot(aq_trim, aes(x = Day, y = Ozone, size = Wind, fill = Month)) + 
      geom_point(shape = 21) +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)") +
      scale_x_continuous(breaks = seq(1, 31, 5))
p6

Again, we can change the colours of these data points, this time using scale_fill_manual.

fill = c("steelblue", "yellowgreen", "violetred1")

p6 <- p6 + scale_fill_manual(values = fill)
p6

Adjusting the size of the data points

The default size of the the data points in a weighted scatterplot is mapped to the radius of the plots. If we want the data points to be proportional to the value of the weighting variable (e.g., a wind speed of 0 mph would have a value of 0), we need to use the scale_size_area.

p6 <- p6 + scale_size_area(max_size = 10)
p6

For our graph, this makes the pattern for Wind a little hard to see. Another way to adjust the size of the data points is to use scale_size and specify a desired range.

p6 <- ggplot(aq_trim, aes(x = Day, y = Ozone, size = Wind, fill = Month)) + 
      geom_point(shape = 21) +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)") +
      scale_x_continuous(breaks = seq(1, 31, 5)) +
      scale_fill_manual(values = fill) +
      scale_size(range = c(1, 10))
p6

Adjusting legend position

To adjust the position of the legend from the default spot of right of the graph, we add the theme option and specify the legend.position = "bottom" argument. We can also change the legend shape using the legend.direction = "horizontal" argument.

p6 <- p6 + theme(legend.position = "bottom", legend.direction = "horizontal")
p6

Changing the legend titles

To change the titles of the two legends, we use the labs option. In order to tell ggplot2 exactly what legend you’re referring to, just have a look in the ggplot option and see what argument you used to create the legend in the first place. In this case we used the size argument for “Wind” and fill for “Month”, so we pass these to labs with our new titles.

p6 <- p6 + labs(size = "Wind Speed (mph)", fill = "Months")
p6

Creating horizontal legends

It looks a little awkward having the two titles sitting on top of each other, as well as taking up unnecessary space. To place the legends next to each other, we use the legend.box = "horizontal" argument in theme. Because the boxes around the legend keys aren’t even in each of the legends, this means the legends don’t align properly. To fix this, we change the box size around the legend keys using legend.key.size. We need to load in the grid package to get this argument to work.

library(grid) 
p6 <- p6 + theme(legend.box = "horizontal", legend.key.size = unit(1, "cm"))
p6

Using the white theme

As explained in the previous posts, we can also change the overall look of the plot using themes. We’ll start using a simple theme customisation by adding theme_bw() after ggplot(). As you can see, we can further tweak the graph using the theme option, which we’ve used so far to change the legend.

p6 <- ggplot(aq_trim, aes(x = Day, y = Ozone, size = Wind, fill = Month)) + theme_bw() +
      geom_point(shape = 21) +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)",
       size = "Wind Speed (mph)", fill = "Months") +
      scale_x_continuous(breaks = seq(1, 31, 5)) +
      scale_fill_manual(values = fill) +
      scale_size(range = c(1, 10)) +
      theme(legend.position="bottom", legend.direction="horizontal",
            legend.box = "horizontal",
            legend.key.size = unit(1, "cm"))
p6

Creating an XKCD style chart

Of course, you may want to create your own themes as well. ggplot2 allows for a very high degree of customisation, including allowing you to use imported fonts. Below is an example of a theme Mauricio was able to create which mimics the visual style of XKCD. In order to create this chart, you first need to import the XKCD font, install it on your machine and load it into R using the extrafont package. These instructions are taken from here:

library(extrafont)

download.file("http://simonsoftware.se/other/xkcd.ttf", 
dest="xkcd.ttf", mode="wb")
system("mkdir ~/.fonts")
system("cp xkcd.ttf~/.fonts")
font_import(paths = "~/.fonts", pattern="[X/x]kcd")
fonts()
loadfonts()

You can then create your graph:

fill <- c("#56B4E9", "#F0E442", "violetred1")

p6 <- ggplot(aq_trim, aes(x = Day, y = Ozone, size = Wind, fill = Month)) + 
      geom_point(shape = 21) +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)",
       size = "Wind Speed (mph)", fill = "Months") +
      scale_x_continuous(breaks = seq(1, 31, 5)) +
      scale_fill_manual(values = fill) +
      scale_size(range = c(1, 10)) +
      theme(axis.line.x = element_line(size=1, colour = "black"),
            axis.line.y = element_line(size=1, colour = "black"),
            axis.text.x=element_text(colour="black", size = 10), 
            axis.text.y=element_text(colour="black", size = 10), 
            legend.position="bottom", legend.direction="horizontal",
            panel.grid.major = element_blank(),
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(),
            panel.background = element_blank(),
            plot.title=element_text(family="xkcd-Regular"), 
            text=element_text(family="xkcd-Regular")) 
p6

Using ‘The Economist’ theme

There are a wider range of pre-built themes available as part of the ggthemes package (more information on these here). Below we’ve applied theme_economist(), which approximates graphs in the Economist magazine.

p6 <- ggplot(aq_trim, aes(x = Day, y = Ozone, size = Wind, fill = Month)) +
      scale_fill_economist() +
      geom_point(shape = 21) +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)", size = "Wind Speed (mph)", fill = "Months") +
      scale_x_continuous(breaks = seq(1, 31, 5)) +
      scale_size(range = c(1, 10)) +
      theme_economist() + 
      theme(axis.line.x = element_line(size=.5, colour = "black"), 
            axis.line.y = element_line(size=.5, colour = "black"), 
            axis.title = element_text(size = 12),
            legend.position = "bottom", legend.direction = "horizontal",
            legend.text = element_text(size = 9),
            legend.title=element_text(face = "bold", size = 9),
            text = element_text(family = "Tahoma"),
            plot.title = element_text(family="Tahoma"))
p6

Creating your own theme

As before, you can modify your plots a lot as ggplot2 allows many customisations. Here we present our original result shown at the top of page.

fill = c("steelblue", "yellowgreen", "violetred1")

p6 <- ggplot(aq_trim, aes(x = Day, y = Ozone, size = Wind, fill = Month)) +
      geom_point(shape = 21) +
      ggtitle("Air Quality in New York by Day") + 
      labs(x = "Day of the month", y = "Ozone (ppb)", size = "Wind Speed (mph)", fill = "Months") +
      scale_x_continuous(breaks = seq(1, 31, 5)) +
      scale_size(range = c(1, 10)) +
      scale_fill_manual(values = fill) +
      theme(axis.line.x = element_line(size=.5, colour = "black"), 
            axis.line.y = element_line(size=.5, colour = "black"), 
            axis.text.x=element_text(colour="black", size = 9), 
            axis.text.y=element_text(colour="black", size = 9),
            legend.position = "bottom", legend.direction = "horizontal",
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), panel.background = element_blank(),
            plot.title = element_text(size = 14, family = "Tahoma", face = "bold"),
            text=element_text(family="Tahoma")) 
p6

Histograms

The first thing to do is load in the data, as below:

rm(list = ls())
library(datasets)
library(ggplot2)

data(airquality)

In this part, we will work towards creating the histogram below. We will take you from a basic histogram and explain all the customisations we add to the code step-by-step.

Basic histogram

In order to initialise a plot we tell ggplot that airquality is our data, and specify that our x axis plots the Ozone variable. We then instruct ggplot to render this as a histogram by adding the geom_histogram() option.

p7 <- ggplot(airquality, aes(x = Ozone)) + geom_histogram()
p7

Adding a normal density curve

We can overlay a normal density function curve on top of our histogram to see how closely (or not) it fits a normal distribution. In this case, we can see it deviates from a normal distribution, showing marked positive skew. In order to overlay the function curve, we add the option stat_function(fun = dnorm), and specify the shape using the mean = mean(airquality$Ozone) and sd = sd(airquality$Ozone) arguments. If you have missing data like we did, make sure you pass the na.rm = TRUE argument to the mean and sd parameters. Finally, you can change the colour using the colour = "red" argument. We will discuss how to customise colours further below.

One further change we must make to display the normal curve correctly is adding aes(y = ..density..) to the geom_histogram option. Note that the normal density curve will not work if you are using the frequency rather than the density, which we are changing in our next step.

p7 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_histogram(aes(y = ..density..)) +
      stat_function(fun = dnorm, colour = "red", 
                    args = list(mean = mean(airquality$Ozone, na.rm = TRUE), 
                                sd = sd(airquality$Ozone, na.rm = TRUE)))
p7

Changing from density to frequency

Let’s go back to the basic plot and lose the function curve. To change the y-axis from density to frequency, we add the aes(y = ..count..) option to geom_histogram.

p7 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_histogram(aes(y = ..count..))
p7

Adjusting binwidth

To change the binwidth, we add a binwidth argument to geom_histogram. In this case, we will make binwidth 5 units of the Ozone variable.

p7 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_histogram(aes(y = ..count..), binwidth = 5)
p7

Customising axis labels

Single line labels

In order to change the axis labels, we have a couple of options. In this case, we have used the scale_x_continuous and scale_y_continuous options, as these have further customisation options for the axes we will use below. In each, we add the desired name to the name argument as a string.

p7 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_histogram(aes(y = ..count..), binwidth = 5) +
      scale_x_continuous(name = "Mean ozone in parts per billion") +
      scale_y_continuous(name = "Count")
p7

Multiline labels

ggplot also allows for the use of multiline names (in both axes and titles). Here, we’ve changed the x-axis label so that it goes over two lines using the \n character to break the line.

p7 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_histogram(aes(y = ..count..), binwidth = 5) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion") +
      scale_y_continuous(name = "Count")
p7

Changing axis ticks

The next thing we will change is the axis ticks. Let’s make the x-axis ticks appear at every 25 units rather than 50 using the breaks = seq(0, 175, 25) argument in scale_x_continuous. (The seq function is a base R function that indicates the start and endpoints and the units to increment by respectively. See help(seq) for more information.) We ensure that the x-axis begins and ends where we want by also adding the argument limits = c(0, 175) to scale_x_continuous.

p7 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_histogram(aes(y = ..count..), binwidth = 5) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 175, 25),
                         limits=c(0, 175)) +
      scale_y_continuous(name = "Count")
p7

Adding a title

To add a title, we include the option ggtitle and include the name of the graph as a string argument.

p7 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_histogram(aes(y = ..count..), binwidth = 5) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 175, 25),
                         limits=c(0, 175)) +
      scale_y_continuous(name = "Count") +
      ggtitle("Frequency histogram of mean ozone")
p7

Changing the colour of the bars

By colour name

To change the line and fill colours of the bars, we add a valid colour to the colour and fill arguments in geom_histogram (note that I assigned these colours to variables outside of the plot to make it easier to change them). A list of valid colours is here.

barfill <- "gold1"
barlines <- "goldenrod2"

p7 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_histogram(aes(y = ..count..), binwidth = 5,
                     colour = barlines, fill = barfill) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 175, 25),
                         limits=c(0, 175)) +
      scale_y_continuous(name = "Count") +
      ggtitle("Frequency histogram of mean ozone")
p7

By HEX code

If you want to go beyond the options in the list above, you can also specify exact HEX colours by including them as a string preceded by a hash, e.g., “#FFFFFF”. Below, we have called two shades of blue for the fill and lines using their HEX codes.

barfill <- "#4271AE"
barlines <- "#1F3552"

p7 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_histogram(aes(y = ..count..), binwidth = 5,
                     colour = barlines, fill = barfill) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 175, 25),
                         limits=c(0, 175)) +
      scale_y_continuous(name = "Count") +
      ggtitle("Frequency histogram of mean ozone")
p7

Colour gradients

You can also add a gradient to your colour scheme that varies according to the frequency of the values. Below is the default gradient colour scheme. In order to do this, you can see we have changed the aes(y = ..count..) argument in geom_histogram to aes(fill = ..count..).

p7 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_histogram(aes(fill = ..count..), binwidth = 5) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 175, 25),
                         limits=c(0, 175)) +
      scale_y_continuous(name = "Count") +
      ggtitle("Frequency histogram of mean ozone")
p7

You can customise the gradient by changing the anchoring colours for high and low. To do so, we have added the option scale_fill_gradient to the plot with the arguments Count (the name of the legend), low (the colour for the least frequent values) and high (the colour for the most frequent values).

p7 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_histogram(aes(fill = ..count..), binwidth = 5) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 175, 25),
                         limits=c(0, 175)) +
      scale_y_continuous(name = "Count") +
      ggtitle("Frequency histogram of mean ozone") +
      scale_fill_gradient("Count", low = "blue", high = "red")
p7

Using the white theme

As explained in the previous posts, we can also change the overall look of the plot using themes. We’ll start using a simple theme customisation by adding theme_bw() after ggplot(). As you can see, we can further tweak the graph using the theme option, which we’ve used so far to change the legend.

barfill <- "#4271AE"
barlines <- "#1F3552"

p7 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_histogram(aes(y = ..count..), binwidth = 5,
                     colour = barlines, fill = barfill) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 175, 25),
                         limits=c(0, 175)) +
      scale_y_continuous(name = "Count") +
      ggtitle("Frequency histogram of mean ozone") +
      theme_bw()
p7

Creating an XKCD style chart

Of course, you may want to create your own themes as well. ggplot2 allows for a very high degree of customisation, including allowing you to use imported fonts. Below is an example of a theme Mauricio was able to create which mimics the visual style of XKCD. In order to create this chart, you first need to import the XKCD font, install it on your machine and load it into R using the extrafont package. These instructions are taken from here:

library(extrafont)

download.file("http://simonsoftware.se/other/xkcd.ttf", 
              dest="xkcd.ttf", mode="wb")
system("mkdir ~/.fonts")
system("cp xkcd.ttf  ~/.fonts")
font_import(paths = "~/.fonts", pattern="[X/x]kcd")
fonts()
loadfonts()

You can then create your graph:

p7 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_histogram(aes(y = ..count..), binwidth = 10,
                     colour = "black", fill = "#56B4E9") +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 175, 25),
                         limits=c(0, 175)) +
      scale_y_continuous(name = "Count") +
      ggtitle("Frequency histogram of mean ozone") + 
      theme(axis.line.x = element_line(size=.5, colour = "black"),
            axis.line.y = element_line(size=.5, colour = "black"), 
            axis.text.x=element_text(colour="black", size = 9), 
            axis.text.y=element_text(colour="black", size = 9),
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), panel.background = element_blank(),
            plot.title = element_text(family = "xkcd-Regular"),
            text=element_text(family="xkcd-Regular"))
p7

Using ‘The Economist’ theme

There are a wider range of pre-built themes available as part of the ggthemes package (more information on these here). Below we’ve applied theme_economist(), which approximates graphs in the Economist magazine.

library(ggthemes)

barfill <- "#4271AE"
barlines <- "#1F3552"

p7 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_histogram(aes(y = ..count..), binwidth = 5, 
                     colour = barlines, fill = barfill) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 175, 25),
                         limits=c(0, 175)) +
      scale_y_continuous(name = "Count") +
      ggtitle("Frequency histogram of mean ozone") +
      theme_economist() +
      theme(axis.line.x = element_line(size=.5, colour = "black"),
            axis.line.y = element_line(size=.5, colour = "black"), 
            axis.text.x=element_text(colour="black", size = 9), 
            axis.text.y=element_text(colour="black", size = 9),
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), panel.background = element_blank(),
            plot.title = element_text(family = "OfficinaSanITC-Book"),
            text=element_text(family="OfficinaSanITC-Book"))
p7

Creating your own theme

As before, you can modify your plots a lot as ggplot2 allows many customisations. Here is a custom plot where we have modified the axes, background and font.

library(grid) 

barfill <- "#4271AE"
barlines <- "#1F3552"

p7 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_histogram(aes(y = ..count..), binwidth = 5, 
                     colour = barlines, fill = barfill) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 175, 25),
                         limits=c(0, 175)) +
      scale_y_continuous(name = "Count") +
      ggtitle("Frequency histogram of mean ozone") +
      theme(axis.line.x = element_line(size=.5, colour = "black"),
            axis.line.y = element_line(size=.5, colour = "black"), 
            axis.text.x=element_text(colour="black", size = 9), 
            axis.text.y=element_text(colour="black", size = 9),
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), panel.background = element_blank(),
            plot.title = element_text(size = 14, family = "Tahoma", face = "bold"),
            text=element_text(family="Tahoma"))
p7

Adding lines

Let’s say that we want to add a cutoff value to the chart (75 parts of ozone per billion). We add the geom_vline option to the chart, and specify where it goes on the x-axis using the xintercept argument. We can customise how it looks using the colour and linetype arguments in geom_vline. (In the the same way, horizontal lines can be added using the geom_hline.)

barfill <- "#4271AE"
barlines <- "#1F3552"

p7 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_histogram(aes(y = ..count..), binwidth = 5,
                     colour = barlines, fill = barfill) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 175, 25),
                         limits=c(0, 175)) +
      scale_y_continuous(name = "Count") +
      ggtitle("Frequency histogram of mean ozone") +
      geom_vline(xintercept = 75, size = 1, colour = "#FF3721", 
                 linetype = "dashed") +
      theme(axis.line.x = element_line(size=.5, colour = "black"),
            axis.line.y = element_line(size=.5, colour = "black"), 
            axis.text.x=element_text(colour="black", size = 9), 
            axis.text.y=element_text(colour="black", size = 9),
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), panel.background = element_blank(),
            plot.title = element_text(size = 14, family = "Tahoma", face = "bold"),
            text=element_text(family="Tahoma"))
p7

Multiple histograms

You can also easily create multiple histograms by the levels of another variable. There are two options, in separate (panel) plots, or in the same plot.

In panel plots

We first need to do a little data wrangling. In order to make the graphs a bit clearer, we’ve kept only months “5” (May) and “7” (July) in a new dataset airquality_trimmed. We also need to convert this variable into either a character or factor variable. We have created a new factor variable Month.f.

In order to produce a panel plot by month, we add the facet_grid(. ~ Month.f) option to the plot. The additional scale = free argument in facet_grid means that the y-axes of each plot do not need to be the same.

airquality_trimmed <- airquality[which(airquality$Month == 5 | 
                                       airquality$Month == 7), ]
airquality_trimmed$Month.f <- factor(airquality_trimmed$Month, 
                                     labels = c("May", "July"))

p7 <- ggplot(airquality_trimmed, aes(x = Ozone)) + 
      geom_histogram(aes(y = ..count..), binwidth = 10,
                     colour = barlines, fill = barfill) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 175, 25),
                         limits=c(0, 175)) +
      scale_y_continuous(name = "Count") +
      ggtitle("Frequency histogram of mean ozone") +
      facet_grid(. ~ Month.f, scales = "free") +
      theme(axis.line.x = element_line(size=.5, colour = "black"),
            axis.line.y = element_line(size=.5, colour = "black"), 
            axis.text.x=element_text(colour="black", size = 9), 
            axis.text.y=element_text(colour="black", size = 9),
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), panel.background = element_blank(),
            plot.title = element_text(size = 14, family = "Tahoma", face = "bold"),
            text=element_text(family="Tahoma"))
p7

In the same plot

In order to plot the two months in the same plot, we add several things. Firstly, in the ggplot function, we add a fill = Month.f argument to aes. Secondly, in order to more clearly see the graph, we add two arguments to the geom_histogram option, position = "identity" and alpha = 0.6. This controls the position and transparency of the curves respectively. Finally, you can customise the colours of the histograms by adding the scale_fill_brewer to the plot from the RColorBrewer package. This blog post describes the available packages.

library(RColorBrewer)

p7 <- ggplot(airquality_trimmed, aes(x = Ozone, fill = Month.f)) + 
      geom_histogram(aes(y = ..count..), binwidth = 10,
                     position="identity", alpha=0.6) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 175, 25),
                         limits=c(0, 175)) +
      scale_y_continuous(name = "Count") +
      ggtitle("Frequency histogram of mean ozone") +
      scale_fill_brewer(palette="Accent") +
      theme(axis.line.x = element_line(size=.5, colour = "black"), 
            axis.line.y = element_line(size=.5, colour = "black"),
            axis.text.x=element_text(colour="black", size = 9), 
            axis.text.y=element_text(colour="black", size = 9),
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), panel.background = element_blank(),
            plot.title = element_text(size = 14, family = "Tahoma", face = "bold"),
            text=element_text(family="Tahoma"))
p7

Formatting the legend

Finally, we can format the legend. Firstly, we can change the position by adding the legend.position = "bottom" argument to the theme option, which moves the legend under the plot. Secondly, we can fix the title by adding the labs(fill="Month") option to the plot.

p7 <- ggplot(airquality_trimmed, aes(x = Ozone, fill = Month.f)) + 
      geom_histogram(aes(y = ..count..), binwidth = 10,
                     position="identity", alpha=0.6) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion", 
                         breaks = seq(0, 175, 25),
                         limits=c(0, 175)) +
      scale_y_continuous(name = "Count") +
      ggtitle("Frequency histogram of mean ozone") +
      scale_fill_brewer(palette="Accent") +
      labs(fill="Month") +
      theme(axis.line.x = element_line(size=.5, colour = "black"),
            axis.line.y = element_line(size=.5, colour = "black"),
            axis.text.x=element_text(colour="black", size = 9), 
            axis.text.y=element_text(colour="black", size = 9), 
            legend.position = "bottom", legend.position = "horizontal",
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), panel.background = element_blank(),
            plot.title = element_text(size = 14, family = "Tahoma", face = "bold"),
            text=element_text(family="Tahoma"))
p7

Density Plots

The first thing to do is load in the data, as below:

rm(list = ls())
library(datasets)
library(ggplot2)

data(airquality)

In this part, we will work towards creating the density plot below. We will take you from a basic density plot and explain all the customisations we add to the code step-by-step.

Basic density plot

In order to initialise a plot we tell ggplot that airquality is our data, and specify that our x axis plots the Ozone variable. We then instruct ggplot to render this as a density plot by adding the geom_density() option.

p8 <- ggplot(airquality, aes(x = Ozone)) + geom_density()
p8

Customising axis labels

In order to change the axis labels, we have a couple of options. In this case, we have used the scale_x_continuous and scale_y_continuous options, as these have further customisation options for the axes we will use below. In each, we add the desired name to the name argument as a string.

p8 <- p8 + scale_x_continuous(name = "Mean ozone in parts per billion") +
      scale_y_continuous(name = "Density")
p8

ggplot also allows for the use of multiline names (in both axes and titles). Here, we’ve changed the x-axis label so that it goes over two lines using the \n character to break the line.

p8 <- p8 + scale_x_continuous(name = "Mean ozone in\nparts per billion")
p8

Changing axis ticks

The next thing we will change is the axis ticks. Let’s make the x-axis ticks appear at every 25 units rather than 50 using the breaks = seq(0, 200, 25) argument in scale_x_continuous. (The seq function is a base R function that indicates the start and endpoints and the units to increment by respectively. See help(seq) for more information.) We ensure that the x-axis begins and ends where we want by also adding the argument limits = c(0, 200) to scale_x_continuous.

p8 <- p8 + scale_x_continuous(name = "Mean ozone in\nparts per billion",
                              breaks = seq(0, 200, 25),
                              limits=c(0, 200))
p8

Adding a title

To add a title, we include the option ggtitle and include the name of the graph as a string argument.

p8 <- p8 + ggtitle("Density plot of mean ozone")
p8

Changing the colour of the curves

To change the line and fill colours of the density plot, we add a valid colour to the colour and fill arguments in geom_density() (note that I assigned these colours to variables outside of the plot to make it easier to change them). A list of valid colours is here.

fill <- "gold1"
line <- "goldenrod2"

p8 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_density(fill = fill, colour = line) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 200, 25),
                         limits=c(0, 200)) +
      scale_y_continuous(name = "Density") +
      ggtitle("Density plot of mean ozone")
p8

If you want to go beyond the options in the list above, you can also specify exact HEX colours by including them as a string preceded by a hash, e.g., “#FFFFFF”. Below, we have called two shades of blue for the fill and lines using their HEX codes.

fill <- "#4271AE"
line <- "#1F3552"

p8 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_density(fill = fill, colour = line) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 200, 25),
                         limits=c(0, 200)) +
      scale_y_continuous(name = "Density") +
      ggtitle("Density plot of mean ozone")
p8

You can also specify the degree of transparency in the density fill area using the argument alpha in geom_density. This ranges from 0 to 1.

p8 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_density(fill = fill, colour = line,
                   alpha = 0.6) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 200, 25),
                         limits=c(0, 200)) +
      scale_y_continuous(name = "Density") +
      ggtitle("Density plot of mean ozone")
p8

Using the white theme

As explained in the previous posts, we can also change the overall look of the plot using themes. We’ll start using a simple theme customisation by adding theme_bw(). As you can see, we can further tweak the graph using the theme option, which we’ve used so far to change the legend.

p8 <- p8 + theme_bw()
p8

Creating an XKCD style chart

Of course, you may want to create your own themes as well. ggplot2 allows for a very high degree of customisation, including allowing you to use imported fonts. Below is an example of a theme Mauricio was able to create which mimics the visual style of XKCD. In order to create this chart, you first need to import the XKCD font, install it on your machine and load it into R using the extrafont package. These instructions are taken from here:

library(extrafont)

download.file("http://simonsoftware.se/other/xkcd.ttf", 
              dest="xkcd.ttf", mode="wb")
system("mkdir ~/.fonts")
system("cp xkcd.ttf  ~/.fonts")
font_import(paths = "~/.fonts", pattern="[X/x]kcd")
fonts()
loadfonts()

You can then create your graph:

p8 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_density(colour = "black", fill = "#56B4E9") +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 200, 25),
                         limits=c(0, 200)) +
      scale_y_continuous(name = "Density") +
      ggtitle("Density plot of mean ozone") +
      theme(axis.line.x = element_line(size=.5, colour = "black"),
            axis.line.y = element_line(size=.5, colour = "black"), 
            axis.text.x=element_text(colour="black", size = 9), 
            axis.text.y=element_text(colour="black", size = 9),
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), panel.background = element_blank(),
            plot.title = element_text(family = "xkcd-Regular"),
            text=element_text(family="xkcd-Regular"))
p8

Using ‘The Economist’ theme

There are a wider range of pre-built themes available as part of the ggthemes package (more information on these here). Below we’ve applied theme_economist(), which approximates graphs in the Economist magazine.

library(ggthemes)
library(grid)

fill <- "#4271AE"
line <- "#1F3552"

p8 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_density(fill = fill, colour = line) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 200, 25),
                         limits=c(0, 200)) +
      scale_y_continuous(name = "Density") +
      ggtitle("Density plot of mean ozone") +
      theme_economist() +
      theme(axis.line.x = element_line(size=.5, colour = "black"),
            axis.line.y = element_line(size=.5, colour = "black"), 
            axis.text.x=element_text(colour="black", size = 9), 
            axis.text.y=element_text(colour="black", size = 9),
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), panel.background = element_blank(),
            plot.title = element_text(family = "OfficinaSanITC-Book"),
            text=element_text(family="OfficinaSanITC-Book"))
p8

Creating your own theme

As before, you can modify your plots a lot as ggplot2 allows many customisations. Here is a custom plot where we have modified the axes, background and font.

library(grid) 

fill <- "#4271AE"
lines <- "#1F3552"

p8 <- ggplot(airquality, aes(x = Ozone)) + 
      geom_density(colour = lines, fill = fill, size = 1) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                            breaks = seq(0, 200, 25),
                            limits=c(0, 200)) +
      scale_y_continuous(name = "Density") +
      ggtitle("Density plot of mean ozone") +
      theme(axis.line.x = element_line(size=.5, colour = "black"),
            axis.line.y = element_line(size=.5, colour = "black"),
            axis.text.x=element_text(colour="black", size = 9), 
            axis.text.y=element_text(colour="black", size = 9), 
            legend.position = "bottom", legend.position = "horizontal",
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), panel.background = element_blank(),
            plot.title = element_text(size = 14, family = "Tahoma", face = "bold"),
            text=element_text(family="Tahoma"))
p8

Adding lines

Let’s say that we want to add a cutoff value to the chart (75 parts of ozone per billion). We add the geom_vline option to the chart, and specify where it goes on the x-axis using the xintercept argument. We can customise how it looks using the colour and linetype arguments in geom_vline. (In the the same way, horizontal lines can be added using the geom_hline.)

fill <- "#4271AE"
line <- "#1F3552"

p8 <- p8 + geom_vline(xintercept = 75, size = 1, colour = "#FF3721", 
                      linetype = "dashed")
p8

Multiple densities

You can also easily create multiple density plots by the levels of another variable. There are two options, in separate (panel) plots, or in the same plot. There are also a couple of variations on these we’ll discuss below.

We first need to do a little data wrangling. In order to make the graphs a bit clearer, we’ve kept only months “5” (May), “6” (June) and “7” (July) in a new dataset airquality_trimmed. We also need to convert this variable into either a character or factor variable. We have created a new factor variable Month.f.

In order to produce a panel plot by month, we add the facet_grid(. ~ Month.f) option to the plot. Note that we’ve also changed the scale of the x-axis to make it fit a little more neatly in the panel format.

airquality_trimmed <- airquality[which(airquality$Month == 5 |
                                       airquality$Month == 6 |
                                       airquality$Month == 7), ]
airquality_trimmed$Month.f <- factor(airquality_trimmed$Month, 
                                     labels = c("May", "June", "July"))

p8 <- ggplot(airquality_trimmed, aes(x = Ozone)) + 
      geom_density(fill = fill, colour = line,
                   alpha = 0.6) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 200, 50),
                         limits=c(0, 200)) +
      scale_y_continuous(name = "Density") +
      ggtitle("Density plot of mean ozone") +
      facet_grid(. ~ Month.f) +
      theme_bw() +
      theme(plot.title = element_text(size = 14, family = "Tahoma", face = "bold"), 
            text = element_text(size = 12, family = "Tahoma"))
p8

An alternative to a panel plot is the volcano plot. This plot swaps the axes (so the variable of interest is on the y-axis and the density is on the x-axis), and reflects the density. In order to create this plot, we replace geom_density with stat_density, and include the arguments aes(ymax = ..density.., ymin = -..density..) and geom = "ribbon" to create a density plot, the usual fill, colour and alpha arguments, and position = "identity". We also need to add a coord_flip() option to the plot.

p8 <- ggplot(airquality_trimmed, aes(x = Ozone)) + 
      stat_density(aes(ymax = ..density..,  ymin = -..density..),
                   geom = "ribbon", 
                   fill = fill, colour = line, alpha = 0.6,
                   position = "identity") +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 200, 25),
                         limits=c(0, 200)) +
      scale_y_continuous(name = "Density",
                         breaks = seq(-0.03, 0.03, 0.03)) +
      ggtitle("Density plot of mean ozone") +
      facet_grid(. ~ Month.f) +
      coord_flip() +
      theme_bw() +
      theme(plot.title = element_text(size = 14, family = "Tahoma", face = "bold"), 
            text = element_text(size = 12, family = "Tahoma"))
p8

In order to plot the three months in the same plot, we add several things. Firstly, in the ggplot function, we add a fill = Month.f argument to aes. Secondly, in order to more clearly see the graph, we add the argument position = "identity" to the geom_density option. This controls the position of the curves respectively. Finally, you can customise the colours of the histograms by adding the scale_fill_brewer to the plot from the RColorBrewer package. This blog post describes the available packages.

library(RColorBrewer)

p8 <- ggplot(airquality_trimmed, aes(x = Ozone, fill = Month.f)) + 
      geom_density(position="identity", alpha=0.6) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 200, 25),
                         limits=c(0, 200)) +
      scale_y_continuous(name = "Density") +
      ggtitle("Density plot of mean ozone") +
      scale_fill_brewer(palette="Accent") +
      theme_bw() +
      theme(plot.title = element_text(size = 14, family = "Tahoma", face = "bold"), 
            text = element_text(size = 12, family = "Tahoma"))
p8

These densities are a little hard to see. One way we can make it easier to see them is to stack the densities on top of each other. To do so, we swap position = "stack" for position = "identity" in geom_density.

p8 <- ggplot(airquality_trimmed, aes(x = Ozone, fill = Month.f)) + 
      geom_density(position = "stack", alpha = 0.6) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 200, 25),
                         limits=c(0, 200)) +
      scale_y_continuous(name = "Density") +
      ggtitle("Density plot of mean ozone") +
      scale_fill_brewer(palette="Accent") +
      theme_bw() +
      theme(plot.title = element_text(size = 14, family = "Tahoma", face = "bold"), 
            text = element_text(size = 12, family = "Tahoma"))
p8

Another way to make it a little easier to see the densities by dropping out the fill. To do this need a few changes. We need to swap the option fill = Month.f in ggplot for colour = Month.f. We add the fill = NA to geom_density, and we’ve also added size = 1 to make it easier to see the lines. Finally, we change the scale_fill_brewer() option for scale_colour_brewer().

p8 <- ggplot(airquality_trimmed, aes(x = Ozone, colour = Month.f)) + 
      geom_density(position="identity", fill = NA, size = 1) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 200, 25),
                         limits=c(0, 200)) +
      scale_y_continuous(name = "Density") +
      ggtitle("Density plot of mean ozone") +
      scale_colour_brewer(palette="Accent") +
      theme_bw() +
      theme(plot.title = element_text(size = 14, family = "Tahoma", face = "bold"), 
            text = element_text(size = 12, family = "Tahoma"))
p8

Formatting the legend

Finally, we can format the legend. Firstly, we can change the position by adding the legend.position = "bottom" argument to the theme option, which moves the legend under the plot. Secondly, we can fix the title by adding the labs(fill="Month") option to the plot.

p8 <- ggplot(airquality_trimmed, aes(x = Ozone, colour = Month.f)) + 
      geom_density(position="identity", fill = NA, size = 1) +
      scale_x_continuous(name = "Mean ozone in\nparts per billion",
                         breaks = seq(0, 200, 25),
                         limits=c(0, 200)) +
      scale_y_continuous(name = "Density") +
      ggtitle("Density plot of mean ozone") +
      scale_colour_brewer(palette="Accent") +
      labs(colour = "Month") +
      theme_bw() +
      theme(legend.position = "bottom",
            plot.title = element_text(size = 14, family = "Tahoma", face = "bold"), 
            text = element_text(size = 12, family = "Tahoma"))
p8

Function Plots

In this part, we will work towards creating the function plot below. We will take you from a basic function plot and explain all the customisations we add to the code step-by-step.

Basic normal curve

In order to create a normal curve, we create a ggplot base layer that has an x-axis range from -4 to 4 (or whatever range you want!), and assign the x-value aesthetic to this range (aes(x = x)). We then add the stat_function option and add dnorm to the function argument to make it a normal curve.

p9 <- ggplot(data.frame(x = c(-4, 4)), aes(x = x)) +
      stat_function(fun = dnorm)
p9

Basic t-curve

stat_function can draw a range of continuous probability density functions, including t (dt), F (df) and Chi-square (dchisq) PDFs. Here we will plot a t-distribution. As the shape of the t-distribution changes depending on the sample size (indicated by the degrees of freedom, or df), we need to specify our df value as part of defining our curve.

p9 <- ggplot(data.frame(x = c(-4, 4)), aes(x = x)) +
      stat_function(fun = dt, args = list(df = 8))
p9

Plotting your own function

You can also draw your own function, as long as it takes the form of a formula that converts an x-value into a y-value. Here we have plotted a curve that returns y-values that are the cube of x times a half:

cubeFun <- function(x) {
    x^3 * 0.5
}

p9 <- ggplot(data.frame(x = c(-4, 4)), aes(x = x)) +
      stat_function(fun = cubeFun)
p9

Plotting multiple functions on the same graph

You can plot multiple functions on the same graph by simply adding another stat_function() for each curve. Here we have plotted two normal curves on the same graph, one with a mean of 0.2 and a standard deviation of 0.1, and one with a mean of 0.7 and a standard deviation of 0.05. (Note that the dnorm function has a default mean of 0 and a default standard deviation of 1, which is why we didn’t need to explicitly define them in the first normal curve we plotted above.) You can also see we’ve changed the range of the x-axis to between 0 and 1.

p9 <- ggplot(data.frame(x = c(0, 1)), aes(x = x)) +
      stat_function(fun = dnorm, args = list(0.2, 0.1)) +
      stat_function(fun = dnorm, args = list(0.7, 0.05))
p9

Customising axis labels

Let’s move forward with this two function graph, and start tweaking the appearance. In order to change the axis labels, we have a couple of options. In this case, we have used the scale_x_continuous and scale_y_continuous options, as these have further customisation options for the axes we will use below. In each, we add the desired name to the name argument as a string.

p9 <- p9 + scale_x_continuous(name = "Probability") +
      scale_y_continuous(name = "Frequency")
p9

Changing axis ticks

The next thing we will change is the axis ticks. Let’s make the x-axis ticks appear at every 0.2 units rather than 0.25 using the breaks = seq(0, 1, 0.2) argument in scale_x_continuous. (The seq function is a base R function that indicates the start and endpoints and the units to increment by respectively. See help(seq) for more information.) We ensure that the x-axis begins and ends where we want by also adding the argument limits = c(0, 1) to scale_x_continuous.

p9 <- p9 + scale_x_continuous(name = "Probability",
                              breaks = seq(0, 1, 0.2),
                              limits=c(0, 1)) +
      scale_y_continuous(name = "Frequency")
p9

Adding a title

To add a title, we include the option ggtitle and include the name of the graph as a string argument.

p9 <- p9 + ggtitle("Normal function curves of probabilities")
p9

Changing the colour of the curves

To change the line colours of the curves, we add a valid colour to the colour arguments in stat_function. A list of valid colours is here.

p9 <- ggplot(data.frame(x = c(0, 1)), aes(x = x)) +
        stat_function(fun = dnorm, args = list(0.2, 0.1),
                      colour = "deeppink") +
        stat_function(fun = dnorm, args = list(0.7, 0.05),
                      colour = "dodgerblue3") +
        scale_x_continuous(name = "Probability",
                              breaks = seq(0, 1, 0.2),
                              limits=c(0, 1)) +
        scale_y_continuous(name = "Frequency") +
        ggtitle("Normal function curves of probabilities")
p9

If you want to go beyond the options in the list above, you can also specify exact HEX colours by including them as a string preceded by a hash, e.g., “#FFFFFF”. Below, we have called two shades of blue for the lines using their HEX codes.

p9 <- ggplot(data.frame(x = c(0, 1)), aes(x = x)) +
        stat_function(fun = dnorm, args = list(0.2, 0.1),
                      colour = "#4271AE") +
        stat_function(fun = dnorm, args = list(0.7, 0.05),
                      colour = "#1F3552") +
        scale_x_continuous(name = "Probability",
                              breaks = seq(0, 1, 0.2),
                              limits=c(0, 1)) +
        scale_y_continuous(name = "Frequency") +
        ggtitle("Normal function curves of probabilities")
p9

Adding a legend

As we have added two separate commands to plot the two function curves, ggplot does not automatically recognise that it needs to create a legend. We can make a legend by swapping out the colour argument in each of the stat_function commands for aes(colour = ), and assigning it the name of the group. We also need to add the scale_colour_manual command to make the legend appear, and also assign colours and a title.

p9 <- ggplot(data.frame(x = c(0, 1)), aes(x = x)) +
        stat_function(fun = dnorm, args = list(0.2, 0.1),
                      aes(colour = "Group 1")) +
        stat_function(fun = dnorm, args = list(0.7, 0.05),
                      aes(colour = "Group 2")) +
        scale_x_continuous(name = "Probability",
                              breaks = seq(0, 1, 0.2),
                              limits=c(0, 1)) +
        scale_y_continuous(name = "Frequency") +
        ggtitle("Normal function curves of probabilities") +
        scale_colour_manual("Groups", values = c("deeppink", "dodgerblue3"))
p9

If you want to use one of the automatic brewer palettes, you can swap scale_colour_manual for scale_colour_brewer, and call your favouite brewer colour scheme. You can see all of the brewer palettes using display.brewer.all(5) As this command doesn’t allow you to assign a title to the legend, you can assign a title using labs(colour = "Groups").

p9 <- ggplot(data.frame(x = c(0, 1)), aes(x = x)) +
        stat_function(fun = dnorm, args = list(0.2, 0.1),
                      aes(colour = "Group 1")) +
        stat_function(fun = dnorm, args = list(0.7, 0.05),
                      aes(colour = "Group 2")) +
        scale_x_continuous(name = "Probability",
                              breaks = seq(0, 1, 0.2),
                              limits=c(0, 1)) +
        scale_y_continuous(name = "Frequency") +
        ggtitle("Normal function curves of probabilities") +
        scale_colour_brewer(palette="Accent") +
        labs(colour = "Groups")
p9

Changing the size of the lines

As you can see, the lines are a little difficult to see. You can make them thicker (or thinner) using the argument size argument within stat_function. Here we have changed the thickness of each line to size 2.

p9 <- ggplot(data.frame(x = c(0, 1)), aes(x = x)) +
        stat_function(fun = dnorm, args = list(0.2, 0.1),
                      aes(colour = "Group 1"), size = 1.5) +
        stat_function(fun = dnorm, args = list(0.7, 0.05),
                      aes(colour = "Group 2"), size = 1.5) +
        scale_x_continuous(name = "Probability",
                              breaks = seq(0, 1, 0.2),
                              limits=c(0, 1)) +
        scale_y_continuous(name = "Frequency") +
        ggtitle("Normal function curves of probabilities") +
        scale_colour_brewer(palette="Accent") +
        labs(colour = "Groups")
p9

Using the white theme

As explained in the previous posts, we can also change the overall look of the plot using themes. We’ll start using a simple theme customisation by adding theme_bw() after ggplot(). As you can see, we can further tweak the graph using the theme option, which we’ve used so far to change the legend.

p9 <- p9 + theme_bw()
p9

Creating an XKCD style chart

Of course, you may want to create your own themes as well. ggplot2 allows for a very high degree of customisation, including allowing you to use imported fonts. Below is an example of a theme Mauricio was able to create which mimics the visual style of XKCD. In order to create this chart, you first need to import the XKCD font, install it on your machine and load it into R using the extrafont package. These instructions are taken from here:

library(extrafont)

download.file("http://simonsoftware.se/other/xkcd.ttf", 
              dest="xkcd.ttf", mode="wb")
system("mkdir ~/.fonts")
system("cp xkcd.ttf  ~/.fonts")
font_import(paths = "~/.fonts", pattern="[X/x]kcd")
fonts()
loadfonts()

You can then create your graph:

p9 <- ggplot(data.frame(x = c(0, 1)), aes(x = x)) +
      stat_function(fun = dnorm, args = list(0.2, 0.1),
                    aes(colour = "Group 1"), size = 1.5) +
      stat_function(fun = dnorm, args = list(0.7, 0.05),
                    aes(colour = "Group 2"), size = 1.5) +
      scale_x_continuous(name = "Probability",
                         breaks = seq(0, 1, 0.2),
                         limits=c(0, 1)) +
      scale_y_continuous(name = "Frequency") +
      ggtitle("Normal function curves of probabilities") +
      scale_colour_brewer(palette="Set1") +
      labs(colour = "Groups") +
      theme(axis.line.x = element_line(size=.5, colour = "black"),
            axis.line.y = element_line(size=.5, colour = "black"), 
            axis.text.x=element_text(colour="black", size = 9), 
            axis.text.y=element_text(colour="black", size = 9),
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), panel.background = element_blank(),
            plot.title = element_text(family = "xkcd-Regular"),
            text=element_text(family="xkcd-Regular"))
p9

Using ‘The Economist’ theme

There are a wider range of pre-built themes available as part of the ggthemes package (more information on these here). Below we’ve applied theme_economist(), which approximates graphs in the Economist magazine.

library(ggthemes)

p9 <- ggplot(data.frame(x = c(0, 1)), aes(x = x)) +
      stat_function(fun = dnorm, args = list(0.2, 0.1),
                    aes(colour = "Group 1"), size = 1.5) +
      stat_function(fun = dnorm, args = list(0.7, 0.05),
                    aes(colour = "Group 2"), size = 1.5) +
      scale_x_continuous(name = "Probability",
                         breaks = seq(0, 1, 0.2),
                         limits=c(0, 1)) +
      scale_y_continuous(name = "Frequency") +
      ggtitle("Normal function curves of probabilities") +
      scale_colour_manual("Groups", values = c("#4271AE", "#1F3552")) +
      theme_economist() +
      theme(axis.line.x = element_line(size=.5, colour = "black"),
            axis.line.y = element_line(size=.5, colour = "black"), 
            axis.text.x=element_text(colour="black", size = 9), 
            axis.text.y=element_text(colour="black", size = 9),
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), panel.background = element_blank(),
            plot.title = element_text(family = "OfficinaSanITC-Book"),
            text=element_text(family="OfficinaSanITC-Book"))
p9

Creating your own theme

As before, you can modify your plots a lot as ggplot2 allows many customisations. Here is a custom plot where we have modified the axes, background and font.

library(grid) 

p9 <- ggplot(data.frame(x = c(0, 1)), aes(x = x)) +
      stat_function(fun = dnorm, args = list(0.2, 0.1),
                    aes(colour = "Group 1"), size = 1.5) +
      stat_function(fun = dnorm, args = list(0.7, 0.05),
                    aes(colour = "Group 2"), size = 1.5) +
      scale_x_continuous(name = "Probability",
                         breaks = seq(0, 1, 0.2),
                         limits=c(0, 1)) +
      scale_y_continuous(name = "Frequency") +
      ggtitle("Normal function curves of probabilities") +
      scale_colour_brewer(palette="Accent") +
      labs(colour = "Groups") +
      theme_bw() +
      theme(axis.line.x = element_line(size=.5, colour = "black"),
            axis.line.y = element_line(size=.5, colour = "black"),
            axis.text.x=element_text(colour="black", size = 9), 
            axis.text.y=element_text(colour="black", size = 9), 
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), panel.background = element_blank(),
            plot.title = element_text(size = 14, family = "Tahoma", face = "bold"),
            text=element_text(family="Tahoma"))
p9

Adding areas under the curve

If we want to shade an area under the curve, we can do so by creating a function that generates a range of normal values with a given mean and standard deviation, and then only retains those values that lie within the desired range (by assigning NAs to everything outside of the range). In this case, we have created a shaded area under the group 1 curve which covers between the mean and 4 standard deviations above the mean (as given by 0.2 + 4 * 0.1). We then add another stat_function command to the graph which plots the area specified by this function, indicates it should be an area plot, and makes it semi-transparent using the alpha argument.

funcShaded <- function(x) {
    y <- dnorm(x, mean = 0.2, sd = 0.1)
    y[x < 0.2 | x > (0.2 + 4 * 0.1)] <- NA
    return(y)
}

p9 <- p9 + stat_function(fun=funcShaded, geom="area", fill="#84CA72", alpha=0.2)
p9

Formatting the legend

Finally, we can format the legend by changing the position. We simply add the legend.position = "bottom" argument to the theme option, which moves the legend under the plot.

p9 <- ggplot(data.frame(x = c(0, 1)), aes(x = x)) +
      stat_function(fun = dnorm, args = list(0.2, 0.1),
                    aes(colour = "Group 1"), size = 1.5) +
      stat_function(fun = dnorm, args = list(0.7, 0.05),
                    aes(colour = "Group 2"), size = 1.5) +
      stat_function(fun=funcShaded, geom="area", fill="#84CA72", alpha=0.2) +
      scale_x_continuous(name = "Probability",
                         breaks = seq(0, 1, 0.2),
                         limits=c(0, 1)) +
      scale_y_continuous(name = "Frequency") +
      ggtitle("Normal function curves of probabilities") +
      scale_colour_brewer(palette="Accent") +
      labs(colour = "Groups") +
      theme_bw() +
      theme(axis.line.x = element_line(size=.5, colour = "black"),
            axis.line.y = element_line(size=.5, colour = "black"),
            axis.text.x=element_text(colour="black", size = 9), 
            axis.text.y=element_text(colour="black", size = 9), 
            legend.position = "bottom", legend.position = "horizontal",
            panel.grid.major = element_line(colour = "#d3d3d3"), 
            panel.grid.minor = element_blank(), 
            panel.border = element_blank(), panel.background = element_blank(),
            plot.title = element_text(size = 14, family = "Tahoma", face = "bold"),
            text=element_text(family="Tahoma"))
p9

Boxplots

The first thing to do is load in the data, as below. We’ll convert Month into a labelled factor in order to use it as our grouping variable.

rm(list = ls())
library(datasets)
library(ggplot2)

data(airquality)
airquality$Month <- factor(airquality$Month, 
                           labels = c("May", "Jun", "Jul", "Aug", "Sep"))

In this part, we will work towards creating the boxplot below. We will take you from a basic boxplot and explain all the customisations we add to the code step-by-step.

Basic boxplot

In order to initialise a plot we tell ggplot that airquality is our data, and specify that our x-axis plots the Month variable and our y-axis plots the Ozone variable. We then instruct ggplot to render this as a boxplot by adding the geom_boxplot() option.

p10 <- ggplot(airquality, aes(x = Month, y = Ozone)) + 
        geom_boxplot()
p10

Customising axis labels

In order to change the axis labels, we have a couple of options. In this case, we have used the scale_x_discrete and scale_y_continuous options, as these have further customisation options for the axes we will use below. In each, we add the desired name to the name argument as a string.

p10 <- p10 + scale_x_discrete(name = "Month") +
        scale_y_continuous(name = "Mean ozone in parts per billion")
p10

ggplot also allows for the use of multiline names (in both axes and titles). Here, we’ve changed the y-axis label so that it goes over two lines using the \n character to break the line.

p10 <- p10 + scale_y_continuous(name = "Mean ozone in\nparts per billion")
p10

Changing axis ticks

The next thing we will change is the axis ticks. Let’s make the y-axis ticks appear at every 25 units rather than 50 using the breaks = seq(0, 175, 25) argument in scale_y_continuous. (The seq function is a base R function that indicates the start and endpoints and the units to increment by respectively. See help(seq) for more information.) We ensure that the y-axis begins and ends where we want by also adding the argument limits = c(0, 175) to scale_y_continuous.

p10 <- p10 + scale_y_continuous(name = "Mean ozone in\nparts per billion",
                              breaks = seq(0, 175, 25),
                              limits=c(0, 175))
p10

Adding a title

To add a title, we include the option ggtitle and include the name of the graph as a string argument.

p10 <- p10 + ggtitle("Boxplot of mean ozone by month")
p10

Changing the colour of the boxes

To change the line and fill colours of the box plot, we add a valid colour to the colour and fill arguments in geom_boxplot() (note that we assigned these colours to variables outside of the plot to make it easier to change them). A list of valid colours is here.

fill <- "gold1"
line <- "goldenrod2"

p10 <- ggplot(airquality, aes(x = Month, y = Ozone)) + 
        geom_boxplot(fill = fill, colour = line) +
        scale_y_continuous(name = "Mean ozone in\nparts per billion",
                           breaks = seq(0, 175, 25),
                           limits=c(0, 175)) +
        scale_x_discrete(name = "Month") +
        ggtitle("Boxplot of mean ozone by month")
p10

If you want to go beyond the options in the list above, you can also specify exact HEX colours by including them as a string preceded by a hash, e.g., “#FFFFFF”. Below, we have called two shades of blue for the fill and lines using their HEX codes.

fill <- "#4271AE"
line <- "#1F3552"

p10 <- ggplot(airquality, aes(x = Month, y = Ozone)) + 
        geom_boxplot(fill = fill, colour = line) +
        scale_y_continuous(name = "Mean ozone in\nparts per billion",
                           breaks = seq(0, 175, 25),
                           limits=c(0, 175)) +
        scale_x_discrete(name = "Month") +
        ggtitle("Boxplot of mean ozone by month")
p10

You can also specify the degree of transparency in the box fill area using the argument alpha in geom_boxplot. This ranges from 0 to 1.

p10 <- ggplot(airquality, aes(x = Month, y = Ozone)) + 
        geom_boxplot(fill = fill, colour = line,
                     alpha = 0.7) +
        scale_y_continuous(name = "Mean ozone in\nparts per billion",
                           breaks = seq(0, 175, 25),
                           limits=c(0, 175)) +
        scale_x_discrete(name = "Month") +
        ggtitle("Boxplot of mean ozone by month")
p10

Finally, you can change the appearance of the outliers as well, using the arguments outlier.colour and outlier.shape in geom_boxplot to change the colour and shape respectively. An explanation of the allowed arguments for shape are described in this article, although be aware that because there is no “fill” argument for outlier, you cannot create circles with separate outline and fill colours. Here we will make the outliers small solid circles (using outlier.shape = 20) and make them the same colour as the box lines (using outlier.colour = "#1F3552").

p10 <- ggplot(airquality, aes(x = Month, y = Ozone)) + 
        geom_boxplot(fill = fill, colour = line, alpha = 0.7,
                     outlier.colour = "#1F3552", outlier.shape = 20) +
        scale_y_continuous(name = "Mean ozone in\nparts per billion",
                           breaks = seq(0, 175, 25),
                           limits=c(0, 175)) +
        scale_x_discrete(name = "Month") +
        ggtitle("Boxplot of mean ozone by month")
p10

Using the white theme

As explained in the previous posts, we can also change the overall look of the plot using themes. We’ll start using a simple theme customisation by adding theme_bw(). As you can see, we can further tweak the graph using the theme option, which we’ve used so far to change the legend.

p10 <- p10 + theme_bw()
p10

Creating an XKCD style chart

Of course, you may want to create your own themes as well. ggplot2 allows for a very high degree of customisation, including allowing you to use imported fonts. Below is an example of a theme Mauricio was able to create which mimics the visual style of XKCD. In order to create this chart, you first need to import the XKCD font, install it on your machine and load it into R using the extrafont package. These instructions are taken from here:

library(extrafont)

download.file("http://simonsoftware.se/other/xkcd.ttf", 
              dest="xkcd.ttf", mode="wb")
system("mkdir ~/.fonts")
system("cp xkcd.ttf  ~/.fonts")
font_import(paths = "~/.fonts", pattern="[X/x]kcd")
fonts()
loadfonts()

You can then create your graph:

p10 <- ggplot(airquality, aes(x = Month, y = Ozone)) + 
        geom_boxplot(colour = "black", fill = "#56B4E9") +
        scale_y_continuous(name = "Mean ozone in\nparts per billion",
                           breaks = seq(0, 175, 25),
                           limits=c(0, 175)) +
        scale_x_discrete(name = "Month") +
        ggtitle("Boxplot of mean ozone by month") +
        theme(axis.line.x = element_line(size = 0.5, colour = "black"), 
              axis.line.y = element_line(size = 0.5, colour = "black"), 
              axis.line = element_line(size=1, colour = "black"), 
              panel.grid.major = element_blank(),
              panel.grid.minor = element_blank(), 
              panel.border = element_blank(), 
              panel.background = element_blank(),
              plot.title=element_text(size = 20, family="xkcd-Regular"), 
              text=element_text(size = 16, family="xkcd-Regular"), 
              axis.text.x=element_text(colour="black", size = 12), 
              axis.text.y=element_text(colour="black", size = 12))
p10

Using ‘The Economist’ theme

There are a wider range of pre-built themes available as part of the ggthemes package (more information on these here). Below we’ve applied theme_economist(), which approximates graphs in the Economist magazine.

library(ggthemes)
library(grid)

fill <- "#4271AE"
line <- "#1F3552"

p10 <- ggplot(airquality, aes(x = Month, y = Ozone)) + 
        geom_boxplot(fill = fill, colour = line) +
        scale_y_continuous(name = "Mean ozone in\nparts per billion",
                           breaks = seq(0, 175, 25),
                           limits=c(0, 175)) +
        scale_x_discrete(name = "Month") +
        ggtitle("Boxplot of mean ozone by month") +
        theme_economist() +
        theme(axis.line.x = element_line(size = 0.5, colour = "black"),
              axis.line.y = element_line(size = 0.5, colour = "black"), 
              legend.position = "bottom", legend.direction = "horizontal",
              legend.box = "horizontal",
              legend.key.size = unit(1, "cm"),
              plot.title = element_text(family="Tahoma"),
              text = element_text(family = "Tahoma"),
              axis.title = element_text(size = 12),
              legend.text = element_text(size = 9),
              legend.title=element_text(face = "bold", size = 9))
p10

Creating your own theme

As before, you can modify your plots a lot as ggplot2 allows many customisations. Here is a custom plot where we have modified the axes, background and font.

library(grid) 

fill <- "#4271AE"
lines <- "#1F3552"

p10 <- ggplot(airquality, aes(x = Month, y = Ozone)) + 
        geom_boxplot(colour = lines, fill = fill,
                     size = 1) +
        scale_y_continuous(name = "Mean ozone in\nparts per billion",
                              breaks = seq(0, 175, 25),
                              limits=c(0, 175)) +
        scale_x_discrete(name = "Month") +
        ggtitle("Boxplot of mean ozone by month") +
        theme_bw() +
        theme(axis.line.x = element_line(size = 0.5, colour = "black"), 
              axis.line.y = element_line(size = 0.5, colour = "black"), 
              panel.grid.major = element_line(colour = "#d3d3d3"), 
              panel.grid.minor = element_blank(), 
              panel.border = element_blank(), panel.background = element_blank(),
              plot.title = element_text(size = 14, family = "Tahoma", face = "bold"),
              text=element_text(family = "Tahoma"), 
              axis.title = element_text(face="bold"),
              axis.text.x = element_text(colour="black", size = 11),
              axis.text.y = element_text(colour="black", size = 9)) 
p10

Boxplot extras

An extra feature you can add to boxplots is to overlay all of the points for that group on each boxplot in order to get an idea of the sample size of the group. This can be achieved using by adding the geom_jitter option.

p10 <- p10 + geom_jitter()
p10

We can see that June has a pretty small sample, indicating that information based on this group may not be very reliable.

Another thing you can do with your boxplot is add a notch to the box where the median sits to give a clearer visual indication of how the data are distributed within the IQR. You achieve this by adding the argument notch = TRUE to the geom_boxplot option. You can see on our graph that the box for June looks a bit weird due to the very small gap between the 25th percentile and the median.

p10 <- ggplot(airquality, aes(x = Month, y = Ozone)) + 
        geom_boxplot(colour = lines, fill = fill,
                     size = 1, notch = TRUE) +
        scale_y_continuous(name = "Mean ozone in\nparts per billion",
                              breaks = seq(0, 175, 25),
                              limits=c(0, 175)) +
        scale_x_discrete(name = "Month") +
        ggtitle("Boxplot of mean ozone by month") +
        theme_bw() +
        theme(axis.line.x = element_line(size = 0.5, colour = "black"), 
              axis.line.y = element_line(size = 0.5, colour = "black"),
              panel.grid.major = element_line(colour = "#d3d3d3"), 
              panel.grid.minor = element_blank(), 
              panel.border = element_blank(), panel.background = element_blank(),
              plot.title = element_text(size = 14, family = "Tahoma", face = "bold"),
              text=element_text(family="Tahoma"), 
              axis.title = element_text(face="bold"),
              axis.text.x=element_text(colour="black", size = 11), 
              axis.text.y=element_text(colour="black", size = 9)) 
p10

Grouping by another variable

You can also easily group box plots by the levels of another variable. There are two options, in separate (panel) plots, or in the same plot.

We first need to do a little data wrangling. In order to make the graphs a bit clearer, we’ve kept only months “July”, “Aug” and “Sep” in a new dataset airquality_trimmed. We’ve also mean-split Temp so that this is also categorical, and made it into a new labelled factor variable called Temp.f.

In order to produce a panel plot by temperature, we add the facet_grid(. ~ Temp.f) option to the plot.

airquality_trimmed <- airquality[which(airquality$Month == "Jul" |
                                       airquality$Month == "Aug" |
                                       airquality$Month == "Sep"), ]
airquality_trimmed$Temp.f <- factor(ifelse(airquality_trimmed$Temp > mean(airquality_trimmed$Temp), 1, 0),
                                    labels = c("Low temp", "High temp"))

p10 <- ggplot(airquality_trimmed, aes(x = Month, y = Ozone)) + 
        geom_boxplot(fill = fill, colour = line,
                     alpha = 0.7) +
        scale_y_continuous(name = "Mean ozone in\nparts per billion",
                           breaks = seq(0, 175, 50),
                           limits=c(0, 175)) +
        scale_x_discrete(name = "Month") +
        ggtitle("Boxplot of mean ozone by month") +
        theme_bw() +
        theme(plot.title = element_text(size = 14, family = "Tahoma", face = "bold"), 
              text = element_text(size = 12, family = "Tahoma"),
              axis.title = element_text(face="bold"),
              axis.text.x=element_text(size = 11)) +
        facet_grid(. ~ Temp.f)
p10

In order to plot the two temperature levels in the same plot, we need to add a couple of things. Firstly, in the ggplot function, we add a fill = Temp.f argument to aes. Secondly, we customise the colours of the boxes by adding the scale_fill_brewer to the plot from the RColorBrewer package. This blog post describes the available packages.

library(RColorBrewer)

p10 <- ggplot(airquality_trimmed, aes(x = Month, y = Ozone, fill = Temp.f)) + 
        geom_boxplot(alpha=0.7) +
        scale_y_continuous(name = "Mean ozone in\nparts per billion",
                           breaks = seq(0, 175, 25),
                           limits=c(0, 175)) +
        scale_x_discrete(name = "Month") +
        ggtitle("Boxplot of mean ozone by month") +
        theme_bw() +
        theme(plot.title = element_text(size = 14, family = "Tahoma", face = "bold"), 
              text = element_text(size = 12, family = "Tahoma"),
              axis.title = element_text(face="bold"),
              axis.text.x=element_text(size = 11)) +
        scale_fill_brewer(palette = "Accent")
p10

Formatting the legend

Finally, we can format the legend. Firstly, we can change the position by adding the legend.position = "bottom" argument to the theme option, which moves the legend under the plot. Secondly, we can fix the title by adding the labs(fill = "Temperature") option to the plot.

p10 <- ggplot(airquality_trimmed, aes(x = Month, y = Ozone, fill = Temp.f)) + 
        geom_boxplot(alpha=0.7) +
        scale_y_continuous(name = "Mean ozone in\nparts per billion",
                           breaks = seq(0, 175, 25),
                           limits=c(0, 175)) +
        scale_x_discrete(name = "Month") +
        ggtitle("Boxplot of mean ozone by month") +
        theme_bw() +
        theme(plot.title = element_text(size = 14, family = "Tahoma", face = "bold"), 
              text = element_text(size = 12, family = "Tahoma"),
              axis.title = element_text(face="bold"),
              axis.text.x=element_text(size = 11),
              legend.position = "bottom") +
        scale_fill_brewer(palette = "Accent") +
        labs(fill = "Temperature")
p10